SlideShare a Scribd company logo
1 of 39
Download to read offline
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
View PDF VersionView Previous ArticleView Next Article
DOI: 10.1039/C2RA01342H (Review Article) RSC Adv. , 2012, 2, 7633-7646
Electrophoretic deposition under
modulated electric fields: a review
Malika Ammam *
Faculty of Science, University of Ontario Institute of Technology, 2000 Simcoe Street North,
Oshawa, ON L1H 7K4, CANADA. E-mail: m78ammam@yahoo.fr; Malika.Ammam@uoit.
ca; Fax: 905-721-3304; Tel: (905)721-8668, ext 3625
Received 21st December 2011 , Accepted 16th May 2012
First published on the web 21st May 2012
Classical electrophoretic deposition (EPD) relies on continuous direct current
(CDC) to deposit charged particles on electrodes. In recent decades,
modulated electric fields such as pulsed direct current (PDC) and alternating
current (AC) have been investigated. This paper reviews EPD under these
modulated electric fields and major applications of the deposited
microstructures. The paper starts with a short overview of EPD principals
such as the electrical double layer of the charged particle, electrophoretic
mobility and main suspension parameters including zeta potential, particle
size, conductivity, viscosity and stability of the suspension. The EPD
mechanisms from the earliest model reported by Hamaker and Verwey to
latest models including Sarkar and Nicholson model and influence of the
electrohydrodynamics and electroosmosis as well as electrode surface and its
electrochemical double layer on the deposition process have been briefly
discussed. Two categories of modulated electric fields, PDC and AC fields
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (1 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
have been addressed with their advantages and disadvantages. It is found that
compared to CDC, PDC offers the advantage of: i) reducing the coalescence
between gas bubbles induced by water electrolysis from aqueous suspensions,
hence yielding deposition of smooth and uniform coatings, ii) reducing
aggregation and disaggregation of nanometer sized particles, leading to
formation of uniform and homogenous deposits and, iii) PDC generates low
change in pH near the electrode, thus it is convenient for deposition of
biochemical and biological species in their highly active states. The main
disadvantage of PDC over CDC lies in the decrease of the deposition yield.
The latter can be more pronounced if low time-pulses are used. Various
categories of AC signals including symmetrical fields with no net DC
component and asymmetrical AC signals without and with net DC component
have been discussed. Overall, the deposition rate under AC fields increases
with polarization time and amplitude. With respect to frequency, the
deposition rate increases with frequency up to certain value then drops at
elevated frequencies. It is noted that deposition under AC signals offers the
possibility to produce superior quality coatings from aqueous suspensions
because electrolysis of water as well as particle orientation during the
deposition could be controlled. From the application standpoint, PDC and
AC, offers new application perspectives such as in biotechnology. Because
under modulated electric fields, EPD can now be accomplished from aqueous
suspensions with low water electrolysis rates, a variety of biochemical and
biological species can be deposited to yield highly active layers suitable for a
wide range of applications including biosensors, biofuel cells and bioreactors.
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (2 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
Malika Ammam
Malika Ammam received her MS degree from the University
of Pierre et Marie CURIE in July 2002 and her PhD from the
University of Paris Sud XI, France in September 2005. From
2006 to 2007, she worked as a research fellow at the
University of Kansas in collaboration with Pinnacle
Technology Inc. (US). From 2007 to 2010, she worked as a
research associate at KU Leuven, Belgium and she is
currently working at the University of Ontario Institute of
Technology in collaboration with Alcohol Countermeasure
Systems Corporation, Canada. Electrophoretic deposition,
electrochemistry, materials, sensing and energy are among
her research projects and interests.
1. Introduction
Electrophoretic deposition (EPD) is an important technology for colloidal coating processes. Fig.
1 illustrates a schematic representation of an EPD cell. Under the influence of direct current (DC)
electric field, the charged colloids or particles suspended or dispersed in a fluid move towards the
electrode and deposit.1–4
Depending on surface charge of the suspended particles, two kind of
EPD can be defined. If the particles are positively charged (Fig. 1), they will move towards the
electrode with the opposite sign, the cathode, and this process is called cathodic EPD. By
contrast, if the dispersed particles are negatively charged, they will be attracted by the positively
charged electrode, the anode, and this process is named anodic EPD.
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (3 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
Fig. 1 Schematic diagram of electrophoretic deposition of
charged particles on the anode of an EPD cell with planar
electrodes.
In EPD, upon application of a potential, a current will flow between the parallel plate electrodes
(Fig. 1). The magnitude of the current that flows is influenced by a variety of system parameters,
including the cell constant, the solution conductivity, and interfacial electrochemical kinetics.
The electric field strength in the suspension (E) is related to the current density (J) and the
conductivity of the suspension (k), which is nothing more than the microscopic formulation of the
Ohm's law (J = kE).
Basic EPD is accomplished from organic suspensions that have several advantages including low
conductivity and good chemical stability of the suspension and absence of the electrochemical
reactions and Joule heating at the electrodes. This leads to formation of high quality coatings.
Nevertheless, the use of organic solvents is associated with many problems including the cost,
volatile, toxicity most of the time and flammability. Furthermore, because organic solvents have
low dielectric constant (dissociation power), this induces a limited particle charge. Thus, high
electric fields strengths are required to move the suspended particles towards the electrode.
EPD from aqueous suspensions is a good alternative for solving many problems associated with
the organic solvents such as the cost and the environmental load. Furthermore, because the
dissociation power of water is high (dielectric constant 80.1), this results in a buildup of a
charge of the particle. Consequently, low electric fields strengths can be used. The main
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (4 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
disadvantage of EPD from aqueous suspensions is water electrolysis. Above the thermodynamic
voltages of water oxidation and reduction,5
electrochemical reactions occur at the electrodes and
generate gases, O2 at the anode and H2 at the cathode (details on the reactions can be found in
section 3.1.1.). The formed gas bubbles can be incorporated in the deposit and yields damaged
and poor quality coatings. To overcome this problem, several approaches have been made.
The first attempted approach was to carry out the EPD process at voltages below the
thermodynamic values of water electrolysis. This provided successful production of alumina
microstructures.6
However, the low applied voltages yielded only low deposition rates that are
limited to small wall thicknesses. Other concepts based on sacrificial electrodes and competitive
reactions have been explored. For example, Chronberg and Händle7
employed zinc (Zn) rollers as
deposition electrodes to compete the oxidation reaction of water with that of Zn, a more facile
reaction. Nonetheless, low deposition rates as well as contamination of the coatings with Zn
limited the process. Materials that store gases such as palladium (Pd) have also been investigated
as cathodes for H2 storage.8
Unfortunately, only small amount of H2 can be stored within the
material. Finally, chemical additives such as hydroquinone were found to be useful for
suppressing O2 evolved at the anode.9,10
But, the concept is only helpful under particular
conditions such as alkaline pH.
One promising method to deal with electrolysis of water during the EPD process from aqueous
suspensions is by using membranes.11–15
A porous and ion-permeable membrane is placed
between the anode and the cathode, hence dividing the EPD cell into two chambers. The
deposition occurs on the membrane itself, but the ions can pass through the membrane pores to
recombine at the electrodes and form gases. The sufficient distance which separates the
membrane from the electrodes allows formation of free-bubble deposits. The membrane based
process was successfully used to deposit different materials such as alumina, silica glass and
zirconia.
Another efficient means to decrease the amount of the evolved gas bubbles at the electrodes and
allow formation of homogenous deposits from aqueous suspensions is to carry out the EPD
process under modulated electric fields such as pulsed direct current (PDC) and alternating
current (AC). Some examples of these signals are shown in Fig. 2. The basic difference between
continuous direct current (CDC) shown in Fig. 2A and PDC of Fig. 2B is that the voltage of a
CDC is roughly constant, whereas the voltage of a PDC wave continually varies, but like a DC
wave, the sign of the voltage is constant. In AC, the voltage continually varies between positive
and negative values. It is worth noting that the rectangular waveform of Fig. 2 constitutes only
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (5 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
one example of a theoretical infinite number of waveforms. In AC, if voltage-time of the positive
and negative half cycles is equal, the waveform is symmetrical with theoretically no net DC
component (Fig. 2C). However, if voltage-time of the two half cycles is different, the AC wave is
asymmetrical and, depending on whether the surface areas of both half-cycles are equal or not,
the wave can be asymmetrical with net DC component (Fig. 2D) or, asymmetrical with no net
DC component (Fig. 2E).
Fig. 2 Schematic representation of some electrical signals: (A)
continuous direct current (CDC), (B) pulsed direct current (PDC),
(C) symmetrical alternating current (AC) with no net DC
component, (D) asymmetrical AC signal with net DC component
and, (E) asymmetrical AC wave with no net DC component.
In recent decades, these modulated electric fields have been investigated not only for EPD of
ceramic and polymer particles but also for biochemical and biological species that are more
sensitive to pH shifts or electrochemical reactions products formed at the electrodes. Because
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (6 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
modulated electric fields generate a low rate of water electrolysis, biochemical and biological
species can be deposited in their highly active states. For instance, EPD of bacterial cells and
enzymes from aqueous solutions under CDC has been reported to some extent.16
However, it is
not clear from the text whether the activity of the species after CDC that generates a high amount
of electrolysis was examined or not.
This paper reviews some selected literature dealing with EPD under modulated electric fields,
PDC and AC, and the main applications of the deposited microstructures. However, first some
necessary reminders and updates about EPD principles should be addressed.
2. EPD principals
2.1. Electrical double layer and electrophoretic mobility
Charged particles in a fluid are surrounded by a cloud of ions. Ions of opposite charge
(counterions) are attracted towards the surface of the charged particle, while ions of similar
charge are pushed away from that surface. This yields a net electrical charge on one side of the
interface and a charge of opposite sign on the other side of the interface, giving rise to what is
called the electrical double layer of the particle. The widely accepted model for the particle
double layer is the Stern model.17
A schematic representation of the particle electrical double
layer with distribution of charged species and potential drop across the double layer in
accordance with Stern model is shown in Fig. 3. If we assume a negatively charged particle, the
ions of opposite charge closest to surface of the particle form what is known as a Stern layer and
the rest of the ions which are distributed more broadly, form what is called the diffuse double
layer (Fig. 3). The particle surface at the plane of shear between Stern and the diffuse layer is
characterized by a potential called zeta potential, ζ, which is involved in nearly all
electrokinetics.18,19
Application of an external electric field can shear away some of the ions
outside the Stern layer and yields a drift and migration of the particle towards the electrode of
opposite charge (Fig. 1).
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (7 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
Fig. 3 Schematic representation of the electric double layer of the
charged particle and potential drop across the double layer. (a)
Surface charge, (b) stern layer, (c) diffuse layers of counter-ions.
Image reproduced from ref. 1 with permission of Elsevier.
The main electrophoretic characteristic of the particle under the influence of the electric field is
called electrophoretic mobility, μeph, which can be defined as the coefficient of proportionality
between the electric field strength, E, and the particle velocity, Veph:19–21
Veph = μephE (1)
In turn, the electrophoretic mobility increases with the particle zeta potential, ζ, and decreases
with the viscosity of the media, η The coefficient of correlation between μ and ζ depends on the
size of the particles. The electrophoretic mobility of small particles defined as having a radius r
much smaller than the Debye length of the counterionic atmosphere (r ≪ 1/k) is described by the
Huckel equation:
μeph = 2εε0ζ/3η (2)
where ε and ε0, are the dielectric permittivity of the media and vacuum, respectively.
The electrophoretic mobility of particles of size much greater than the Debye length of the
counterionic layer (r ≫ 1/k) is given by the Helmholtz–Smoluchowski equation:
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (8 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
μeph = εε0ζ/η (3)
The displacement of a particle for a finite time Δt under uniform DC electrophoresis can
reasonably be defined as21
:
xDC = μephEDCΔt + x0 (4)
where the constant x0 determines the initial location of the particle.
2.2. Key suspension parameters
EPD is a two-step mechanism. First, the particles must migrate to the deposition electrode under
the action of an electric field and, second, the particles must coagulate and deposit on the
electrode (Fig. 1). There are a number of suspension parameters that influence the EPD process
as well as the quality of the deposited coating. Some of the important ones are discussed below.
2.2.1. Zeta potential. Zeta potential is a key parameter. The dispersed particles are required to
have an elevated and a uniform surface charge, which will determine their stability in the
suspension. The stability of the charged particles is essentially governed by the sum of the
attractive and the repulsive forces between the particles, mainly electrostatic and van der Waals
in nature. To prevent agglomeration between particles, high particle charge is required to create
high electrostatic repulsion. By contrast, if the particle charge is low, the particles will coagulate.
The particle charge or zeta potential can be controlled by various charging agents such as acids,
bases, or specifically adsorbed polyelectrolytes.22
However, before using charging agents to
increase the charge of the suspended particles, the first common step in suspension preparation is
powder washing. This step allows the removal of any residual impurities that are incorporated
with the powder and may affect the stability of the suspension, thus the deposition characteristics.
Basu et al.23
reported that unwashed powder led to an unstable suspension, which in turn led to
lower deposition yields and a decrease in green density of the deposit by about 15–25%. The
problem was solved by repetitive washing of the powder with deionized water. Also, during the
washing process, significant reduction in the conductivity of the supernatant was observed.23
Hence, it can be concluded that the washing process is an important factor in suspension stability.
While the washing process can easily be accomplished with inorganic materials such as ceramic
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (9 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
particles,23
for biomolecules and biological cells, this step might be difficult. Because enzymes
and biological cells usually contain salts for electroneutrality, their dispersion, even in ultrapure
water gives rise to high conductivity suspensions, which in turn may affect their zeta potential as
well as the suspension stability.24–26
The charge on a biomolecule such as enzymes, proteins or biological cells arises from the
ionization of the functional groups present within the biomolecule. In proteins or enzymes, these
groups carried out by essentially the amino acids residues give rise to either positive or negative
charges. In acidic pH, the net charge of the enzymes is usually positive, whereas in alkaline pH,
the charge is negative. At a certain pH, enzymes will have no net charge, called isoionic point,
which is around pH 4 for glucose oxidase for example. At neutral pH, enzymes such as glucose
oxidase are negatively charged and the zeta potential of enzymes depends largely on the
dissolving media. Matsumoto et al.27
measured the zeta potential of glucose oxidase dissolved in
high ionic strength phosphate buffer solution as −0.4 mV. This led to practically no
electrophoretic mobility of the enzyme. This problem can be solved if the enzyme is dissolved in
ultrapure water. Ammam and Fransaer24
measured the zeta potential of glucose oxidase dissolved
in ultrapure water containing low amount of NaOH as charging agent as −10.7 mV. The latter led
to a net electrophoretic mobility of the enzyme when asymmetrical AC fields are applied to form
thick deposits on the electrode.
For biological cells, the washing procedure is easier than for enzymes and proteins because cells
can be dispensed in water and filtered off to remove the excess salts. Consequently, adequate zeta
potentials of cells suspended in water have been recorded.16,28,29
A typical example on how zeta
potential varies with pH of the suspension is shown in Fig. 4 for E. Coli microorganism and
inclusion bodies.16
The isoionic point of these species is located at pH 3–4. At higher pH, the
species are negatively charged, whereas at lower pH, the species are positively charged. The
charge or zeta potential of the species increases when pH is moved away from the isoionic point.
Dependence of zeta
potential on pH for a
suspension of pure E. Coli
bacteria and a suspension of
pure inclusion bodies.
Image reproduced from ref.
16 with permission of
Elsevier.
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (10 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
Fig. 4 Dependence of zeta potential on pH for
a suspension of pure E. Coli bacteria and a
suspension of pure inclusion bodies. Image
reproduced from ref. 16 with permission of
Elsevier.
2.2.2. Particle size. Particle size is an important parameter in the EPD process. For stable
suspension, it is important that the dispersed particles remain well dispersed and stable to yield
homogenous and uniform deposits. For ceramic particles, it is reported that the optimal range of
particle size lies between 1–20 μm.30
The problem with larger sizes is that the particles tend to
sediment under the gravitational forces leading in vertical cells to thick deposits on the bottom
and thin films on top. Likewise, very small particles tend to aggregate and thus yield
inhomogeneous deposits.
2.2.3. Conductivity and viscosity of the suspension. In EPD, the amount of the deposited
particles is related to the strength of the electric field. The applied electric field between the
anode and cathode is not only carried by the charged particles but mostly by the free coexisting
ions (electrolyte). On the other hand, the amount of the coexisting ions determines the
conductivity of the suspension, an important factor in EPD. If the conductivity of the suspension
is too high, i.e., the amount of the free ions is considerable, the particle mobility decreases
because the zeta potential is reduced.26
By contrast, if the conductivity is too low, the suspension
will be resistive, leading to loss in stability.25
In turn, the conductivity is related to dielectric constant or dissociation power of the solvent. It is
reported that optimal deposition rates are obtained with liquids having dielectric constant in the
range of 12–25,31
specifically associated with organic solvents. With liquids having high
dissociation power such as water (dielectric constant 80.1 at 20 °C), the amount of ions in the
suspension must be very low in order to yield stable suspension, hence high deposition rate. Also,
viscosity accounts in EPD process. The amount of the dispersed particles and the pH affect the
viscosity of the suspension.25,32
Low viscosities are required for successful EPD and optimal
dispersant concentration can experimentally be determined.32
2.2.4. Suspension stability. A stable suspension with well-dispersed and controlled surface
charge is essential for successful EPD.25
The stability of the suspension is characterized by the
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (11 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
rate and tendency of the charged particles to undergo or avoid flocculation. The suspension
stability depends on several factors such as size of the particles, their zeta potential, Debye length
of the solution as well as the presence of adsorbed species. Average sized particles with uniform
surface charge tend to stay suspended for long periods due to Brownian motions. Bigger sized
particles tend to sediment because of the strong gravitational forces, thus require continuous
hydrodynamic agitation to stay in the suspension. Stable suspension shows no flocculation or
sedimentation of the particles. However, if the suspension is too stable, meaning that the
repulsive forces between the particles are too strong, the electric field will not be able to
overcome these forces and move the particles towards the electrode, thus there will be no
deposition. Near the electrode, if the suspension remains stable, there will be no deposition.
Fortunately, presence of other phenomena such as electrochemical reactions, electroosmosis and
electrohydrodynamic flows induce instability near the electrode and cause the particles to
fluctuate and precipitate.
2.3. EPD mechanisms
After migration of the charged particles from the bulk to the electrode of opposite charge, the
next step in EPD process is the coagulation and deposition. Although EPD is known since the
19th century, the deposition mechanisms are not fully understood and still under debate. Several
theories have been proposed.
The earliest dates back to 1940s. Hamaker and Verwey33
suggested that deposition is due to
accumulation of the charged particles on the electrode under the action of the applied electric
field. Nevertheless, the proposed mechanism is more useful for deposition of particles on a
membrane placed between two electrodes, rather than for deposition on the electrode.
In 1992, Grillon et al.34
suggested that EPD occurs by particle charge neutralization. The charged
particle approaching the electrode neutralizes upon contact with the opposite charge of the
electrode and precipitate. The drawback of this theory is that the deposition is limited to a
monolayer and this cannot explain the formation of thick coatings.
Few years later, Koelmans35
and later De and Nicholson36
proposed that deposition is governed
by electrochemical particle coagulation. Due to electrochemical reactions at the electrodes during
the EPD process, the ionic strength near the electrode surface would increase compared to bulk.
This induces a reduction of the repulsive forces between particles near the electrode, which in
turn lowers zeta potential and induces precipitation. This theory is useful to explain deposition of
particles from suspensions containing water but not EPD from organic suspensions since no
electrochemical reactions occur.
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (12 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
To overcome the problem dealing with coagulation in absence of the electrochemical reactions,
Sarkar and Nicholson17
suggested that deposition occurs through the double layer distortion and
thinning, followed by coagulation of the particles on the electrode. As illustrated in Fig. 5, three
main successive steps take place:
i) When the charged particle that is surrounded by the diffuse double layer is subjected to an
electric field, it undergoes a distortion and becomes thinner ahead and wider behind.
ii) During the migration of the charged particle, ions of similar charge will move in same
direction of the particle and can react with the counter ions accompanying the charged particle.
The latter induces a thinning of the double layer of the particle.
iii) Because the double layer of the particle is now thinner, it can easily approach another particle
with also a thinner double layer and, if the contact is close enough to favor van der Waals
attractive forces, the deposition occurs.
So far, no experimental data have yet been presented to support this theory. However, thanks to
imagery techniques, experimental data are now available on how the particles aggregate on the
electrode. The aggregation is modeled by various mechanisms such as electrohydrodynamics37
and electroosmosis.38,39
The action of an electric field on charge of the particle diffuse layer gives
rise to the electroosmotic flow, while action of an electric field on charge induced by the electric
field on the electrode gives rise to the electrohydrodynamic flow. For electroosmosis, thickness
of the electrical double layer of the particle, particularly, the diffuse layer is a key determinant of
the electroosmotic forces. A thick diffuse layer yields significant electroosmotic forces, while a
thin diffuse layer gives rise to negligible electroosmotic forces.39
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (13 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
Fig. 5 Electrical double layer distortion and thinning mechanism
for electrophoretic deposition. Image reproduced from ref. 17
with permission of Wiley & Sons.
Also, the electrode surface and its electrochemical double layer play an important role in the
deposition process.5,40
Polarizable electrodes create a substantial potential drop in the
electrochemical double layer of the electrode, thus most of the current is capacitive.
Consequently, the electric field strength reduces in the bulk of the suspension and induces
instability. By contrast, non-polarisable electrodes generate minimum drop current and most of
the current is Faradaic. This induces an effective electric strength in the bulk of the suspension.
Prieve et al.40
have recently reviewed 2D assembly of particles under DC and AC electric fields
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (14 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
and emphasized the role of the electrochemical double layer of the electrode in the deposition
process.
3. EPD under modulated electric fields
3.1. PDC fields
The advantages of PDC shown in Fig. 2B over CDC of Fig. 2A for EPD of charged particles can
be summarized as:
i) PDC significantly reduces the coalescence between gas bubbles induced by water electrolysis.
Thus, yields deposition of smooth and uniform coatings.
ii) PDC reduces aggregation between nanometer sized particles, leading to formation of uniform
and homogenous deposits.
iii) PDC generates low change in pH near the electrode. Hence, is convenient for deposition of
biochemical and biological species in their highly active states.
3.1.1. Reduction in coalescence between gas bubbles. PDC has been investigated for EPD of
ceramic particles,41–46
polymers,47
carbon nanotubes48
and enzymes.49
In all cases, low rates of
gas bubbles have been noticed when PDC is used. Fig. 6 depicts typical topographies of alumina
deposits produced from aqueous suspensions using CDC and PDC with various time-pulses. It
can be seen that under CDC, the deposits are porous and inhomogeneous. This is due to water
electrolysis, which forms gases, O2 at the anode and H2 at the cathode, following the reactions I
to IV:5
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (15 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
Fig. 6 Surface morphology of deposits obtained by PDC EPD at
constant voltage mode of 20 V (A) and at constant current mode of
0.004 A (B). Image reproduced from ref. 46 with permission of
Elsevier.
Anode: 2H2O = O2 + 4H+ + 4e− (Eo = −1.23 V vs. NHE) (I)
4OH− = O2 + 2H2O + 4e− (Eo = −0.40 V vs. NHE) (II)
Cathode: 2H+ + 2e− = H2 (Eo = 0 V vs. NHE) (III)
2H2O + 2e− = H2 + 2OH− (Eo = −0.83 V vs. NHE) (IV)
The dominant reaction would of course depend on whether the aqueous suspension contains
sufficient amounts of H+, OH− or only water. For example, if the solution contains a sufficient
amount of OH−, OH− would be the first species to be oxidized into O2 at the anode because the
reaction requires less voltage (−0.4 V) than that of water oxidation (−1.23 V). Similarly, if H+
were added to the aqueous suspension, H+ would be the first species to be reduced into H2 at the
cathode because the reaction requires 0 V compared to reduction of water molecules (−0.83 V).
However, if pure water is used as a fluid suspension, after the reduction and oxidation of the
small amount of H+ and OH− present at the concentration of 10−7 M, water molecule will be the
main species to be oxidized at the anode and reduced at the cathode with voltages of −1.23 V and
−0.83 V, respectively.
During EPD process, the generated gas bubbles can be incorporated in the deposit, and results in
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (16 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
porous morphologies (CDC of Fig. 6). By comparison, under PDC, the number and size of the
pores can be reduced if time-pulses are decreased. Theoretically, once the thermodynamic
voltages of water electrolysis are reached, water starts to decompose into O2 and H2.
Nevertheless, depending on the reaction conditions such as nature of the electrode material,
nature of the electrolyte and its concentration etc., the potentials may shift from the
thermodynamic values. The latter defines the kinetics of water electrolysis reactions.
Besra et al.46
measured larger shifts in pH near the electrode using CDC compared to PDC. This
may suggest that PDC induces low rates of electrolysis compared to CDC. However, taking into
account the total polarization time (ON + OFF) used for PDC that is higher than that used for
CDC since CDC has no OFF-time, it is possible to propose that using PDC, the reaction products
formed during the ON-time diffuse towards the bulk solution during the OFF-time, inducing less
change in pH near the electrode. Thus, it maybe concluded that unless extremely low time-pulses
are used,50
PDC probably do not generate low rates of electrolysis, but more appropriately it
minimizes coalescence between gas bubbles, thus preventing formation of larger ones.
Fig. 7 supports this claim. It shows a comparison between SEM images of polypyrrole (PPy)
coatings on glassy carbon (GC) substrates produced by electropolymerization of pyrrole
monomer from low conductivity solutions using CDC (Fig. 7A, 7B and 7C) and PDC (Fig. 7D).51
The same deposition time is used for all coatings. In addition, 10 s is used as time-pulse for PDC
that is large enough to induce formation of gas bubbles since micro-meter sized bubbles were
observed even with pulses of 0.1 ms.50
Fig. 7A, 7B and 7C clearly depict rough and
inhomogeneous topographies of PPy deposits under CDC. This is due to the large amount of gas
bubbles incorporated in the coatings. More importantly, Fig. 7C clearly shows that under CDC,
the gas bubbles coalesce and when maximum volumes are reached, the bubbles explode and form
patterns that can be described as “open flowers”. By comparison, the topography of PPy coating
obtained by means of PDC is smoother and homogenous (Fig. 7D). Interruption of the field
during OFF-time for PDC breaks apart most of the tiny formed bubbles. Hence, prevent their
coalescence during the next ON-time polarization.
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (17 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
Fig. 7 SEM images of electrodeposited polypyrrole (PPy) from
pyrrole aqueous solutions using CDC (A, B, C) and PDC (D) at 4 V
vs. Ag/AgCl for equal ON-time deposition mode. Part of the image
reproduced from ref. 51 with permission of Elsevier.
3.1.2. Reduction of aggregations between particles. The second advantage of PDC over CDC
is that PDC prevents the particles near the electrode from aggregation. Fig. 8A and 8B depict
SEM images of 2D polystyrene particles deposited by means of PDC and CDC, respectively.47
While aggregation between particles can be observed with CDC (Fig. 8B), the monolayer formed
by means of PDC depicts more independent particles (Fig. 8A). Under PDC, the decrease in
aggregation between the particles can be assigned to:
i) Reduction in the electroosmotic flow that is induced near the electrode (Fig. 8C). In other
words, when an electric field is applied between the anode and the cathode, the charged particles
move towards the electrode of opposite charge. As the particles approach the electrode, the
electroosmotic forces induced by the electric field interfere within the Debye length range and
bend the electrophoretic forces. This causes their aggregation in CDC. Under PDC, the
electroosmotic flow stops during the OFF-time and when the next ON-time starts, the particles
near the electrode move under electrophoresis, without significant interference from
electroosmosis and thus deposit independently.47
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (18 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
ii) Reduction in coalescence between the formed gas bubbles. In other words, under CDC,
electrolysis of water induces large-sized bubbles that may generate a pressure on the surrounding
particles and push them away. As a result, the particles will be gathered in between the formed
gas bubbles and aggregate as in Fig. 8B. By comparison, because PDC prevent gas bubbles from
coalescence and reduce their size, the pressure applied by the formed bubbles should also be
reduced. This yields deposition of independent particles at 2D (Fig. 8A) and 3D.43
Single-size deposit particles
by PDC (A) and CDC
polarisation (B). All
particles are deposited at
3.3 V cm−1 for 2 min. (C)
Illustration of on-going
deposit particles during
EPD. The effect of
electrokinetic phenomena is
to induce the on-going
particles as they approach
the substrate. The off-mode
condition reduces the effect
of electroosmosis on an
incoming deposit particle
(particle 2). Image
reproduced from ref. 47
with permission of Elsevier.
Fig. 8 Single-size deposit particles by PDC (A)
and CDC polarisation (B). All particles are
deposited at 3.3 V cm−1 for 2 min. (C)
Illustration of on-going deposit particles during
EPD. The effect of electrokinetic phenomena is
to induce the on-going particles as they
approach the substrate. The off-mode condition
reduces the effect of electroosmosis on an
incoming deposit particle (particle 2). Image
reproduced from ref. 47 with permission of
Elsevier.
3.1.3. Preservation of the activity of deposited biomolecules. PDC is advantageous over CDC
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (19 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
for EPD of biomolecules such as enzymes.49
Because PDC yields low change in pH near the
electrode,46
consequently, the activity of the deposited enzyme is preserved. Ammam and
Fransaer49
noticed a decrease in activity of the deposited enzyme by 25% when they switched
from PDC to CDC under the same conditions.
3.1.4. Disadvantages of PDC over CDC. The main disadvantage of PDC over CDC is the
decrease in the deposition yield. The latter can be more pronounced if low time-pulses are used as
depicted in Fig. 6.42,46
Although the deposition mechanisms under PDC still under investigation,
if sufficient time-pulses are employed, accumulation of the particles on the electrode is attributed
to the strong inertia forces induced by the PDC field. This results in migration of the particles
near the electrode for a few more seconds following the OFF-time mode to reach the electrode
and deposit without bubbles.46
The reduction in the deposition yield using PDC is attributed to
the low change in pH near the electrode, which slow down the charged particles located near the
electrode to reach their isoelectric point and precipitate.35,36,46
3.2. AC fields
While in DC fields the electric charge flows only in one direction, in AC fields the movement of
the electric charge periodically reverses direction between the positive and negative (Fig. 2). As a
consequence, under an AC field the dynamic of particles are much more complicated than in DC.
Thus, analysis of the experimental observations is often difficult because there are a number of
phenomena and forces that arise from the interaction of the AC field with the suspended particle,
and this is influenced by a range of parameters including frequency, particle size, electrolyte
conductivity, electric field distribution, and whether the current passes through the capacitance of
the electrode double layer or, through the electrochemical reaction.40,52–60
Some of the forces are
well-studied and documented in literature such as electrophoresis,61–63
dielectrophoresis,64–67
electrorotation68,69
and travelling-wave dielectrophoresis.70
The basic difference between these
forces is schematically depicted in Fig. 9.
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (20 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
Fig. 9 Schematic representation of a charged particle under the
influence of electrophoresis (A), dielectrophoresis (B),
electrorotation (C) and travelling wave dielectrophoresis (D).
Electrophoresis. In electrophoresis (Fig. 9A), a dispersed charged particle in a fluid moves and
migrates under the action of a uniform electric field towards the electrode of opposite charge.
Dielectrophoresis. If the electric field is not uniform as illustrated in Fig. 9B, the interaction
between the induced dipole and the non-uniform electric field generates a force. Due to presence
of the electric field gradient, these forces are not equal in magnitude and generate net movement
of the charged particle under dielectrophoresis.
Electrorotation. If the electric field is rotating as depicted in Fig. 9C, a dipole is induced across
the particle, which will simultaneously rotate with the electric field. If the angular velocity of the
rotating field is large enough, this will require certain time to form a dipole on the particle, which
will lag behind the field. The non-zero angle between the field and the dipole induces the particle
to rotate in the field and gives rise to electrorotation.
Travelling wave dielectrophoresis. Travelling wave dielectrophoresis is a linear form of
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (21 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
electrorotation. As displayed in Fig. 9D, instead of a circular arrangement, the electrodes are
arranged in a linear manner with 90° phase shift from each other. An electric field wave is
produced between the electrodes and interaction between this wave and the polarizable particle
induces a dipole that will move with the electric field. If the field wave is strong enough, the
dipole will lag behind the field just like in electrorotation. However, because the electric wave is
travelling in linear instead of circular manner, a force, rather than a torque will be induced, thus
leading to a drift of the particle from one electrode to another.
Therefore, as one can imagine, under AC fields, various phenomena could occur simultaneously
and the deposition mechanisms are often unclear. For example, at low frequencies, the interaction
between the charged particle and the field gives rise to electrophoresis. AC field also produces a
frequency dependent dipole on a polarisable suspended particle and depending on the field
distribution; interaction between the dipole and the electric field can generate dielectrophoresis,
electrorotation and travelling wave dielectrophoresis (Fig. 9). Furthermore, if the AC field is
strong enough, it induces a fluid flow and heating at the electrodes. The AC field can interact
with the fluid to produce electrohydrodynamic and electroosmotic forces as well as
electrothermal due to Joule heating. The resulting fluid flow may induce a drag force on the
particle and thus a motion. Depending on the frequency and the ionic conductivity (electrolyte),
the electrohydrodynamic flow may induce aggregation or separation between the suspended
particles near the electrode. At high frequencies, electrothermal fluid flow competes with the
dielectrophoretic forces and electrohydrodynamics account. At low frequencies, AC
electroosmotic flow dominates and this is strong even at low potentials. At intermediate
frequencies, both electrohydrodymics and electrosmosis are active. On top of all the applied
forces, particle–particle interaction and Brownian motion occur continuously.
Because of the complicated dynamics of particles under AC fields, the formulas describing the
displacement of the charged particles in the AC field are also complicated if compared to the
simple DC formula shown in equation (4). The displacement of charged particles in AC fields
will depend essentially on nature of the AC waveforms (sine, triangular, rectangular etc.) as well
as the symmetry or asymmetry of the signal, which will define the mathematical formulas.20,21
For example, in case of an harmonically oscillating electric field, the amplitude of the peak-to-
peak displacement, xAC, of the charged particle is reported as:21
xAC = −[μeph/EAC/sin(ωt)]/ω + x1 (5)
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (22 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
where EAC is the peak to peak amplitude, ω is the applied angular frequency, μeph is the
electrophoretic mobility and x1 determines the center of the trajectory.
3.2.1. Symmetrical AC fields with no net DC component. Symmetrical AC-electric fields have
been used since the 19th century for EPD of charged particles. This can be found in a large
number of patents typically for industrial applications such as electro-coating of paint based
polymers and copolymers.71
A typical example of symmetrical AC waveform that generates no
net DC component is shown in Fig. 2C. What theoretically can be predicted using symmetrical
and uniform AC waveforms is that at low frequencies and during the first half-cycle of the
period, the charged particle moves a certain distance, d. During the other half-cycle, the particle
changes its direction back to its original position, −d. Consequently, the particle oscillates around
a fixed spot in the fluid between the two electrodes and its net migration becomes zero.20,72
Therefore, it can be concluded that symmetrical and uniform AC signals would not be
appropriate for an efficient EPD. Nevertheless, a large number of scientists have succeeded to
deposit thin and even thick coatings using symmetrical waves. In view of this, in 1979, Ul'berg et
al.73
deposited weakly charged submicron oligomeric epoxy resin particles. Later, Hirata et al.74
reported EPD of alumina particles under symmetrical sine waves from aqueous suspensions at
voltage of 6 V and frequencies of 0.12, 1, and 10 kHz. In the past decade, Poortinga et al.75
investigated symmetrical AC signals for EPD of spherical and rod-shaped bacterial cells and
noticed that the bacterial cells adhere and deposit on the electrode if sufficiently high currents are
used.
Although the deposition mechanisms under these signals are not fully understood, the formed
monolayers have been attributed by Ul'berg et al.73
and Hirata et al.74
to diffusion (inertia free)
since the particles were observed to coagulate on the electrode instantly. On the other hand, other
phenomena such as electrohydrodynamic and electroosmotic forces may account in the
deposition process. In this context, Sides54
reported that when the frequency changes, the
interaction strength between the particles near the electrode can reach its maximum and it can
even reverse attractive to repulsive forces and vice versa leading to aggregation of the particles
on the electrode.54
So far, when uniform and symmetrical AC signals are used, low deposition rates that are limited
to monolayers were usually depicted.28,74,75
There are some reported contradictory observations,
where, using symmetrical or uniform AC signals, thick deposits were obtained. For example,
Gardeshzadeh et al.76
deposited thick films of multiple walled carbon nanotubes using square and
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (23 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
sine waves at frequencies of 1–1000 Hz as well as thick films of SnO2.77
Heidari et al.78,79
followed the procedure by Gardeshzadeh and obtained thick films. Also, Riahifar et al.72,80
employed similar category of electrodes as Heidari and deposited thick TiO2 films.
According to theoretical predictions, these symmetrical signals should not form thick deposits.
The latter might be related to the setup used to carry out the deposition. Non-planar and non-
parallel electrodes have been employed. An example of the electrodes configuration is illustrated
in Fig. 10. This configuration suggest generation of non-uniform electric fields which will give
rise to not only electrophoresis, but to eventually other forces such as dielectrophoresis and
travelling wave dielectrophoresis of the particles from one electrode to another.
Fig. 10 Optical microscopy image of the electrode configuration
used by Heidari et al.79
to deposit WO3 particles. Because space
between the electrodes is only hundreds of μm, the particles have
connected the electrodes together. Image reproduced from ref. 79
with permission of Springer.
The main characteristics of EPD under symmetrical AC waveforms is that the deposition rate
increases by reducing the frequency72,73,75
and increasing the voltage.72,73
Also, the deposition
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (24 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
yield augments with the polarization time then reaches a saturation plateau.73,77
3.2.2. Asymmetrical AC field with net DC component. A typical example of asymmetrical AC
wave with net DC component is shown is Fig. 3D. Because the surface area voltage–time (E–t) of
the positive and negative half-cycles are not equal, a DC component is induced. This leads to a
net drift of the charged particle towards the electrode of opposite charge. Furthermore, under this
category of signals, inertia forces could also be an important driving force for migration of the
particles because, during the fast voltage change from the positive to the negative signal and vice
versa, the particles are accelerated and they cannot slow down open the reverse signal. The latter
has been experimentally observed by Nold and Clasen,81
who recorded at the output a
supplementary peak every third peak that has initially not been programmed.
The advantage of the asymmetrical AC signal with net DC over pure DC consists of producing
superior quality coatings because electrolysis as well as particle orientation during deposition
could be controlled to some extent. In view of this, Shindo et al.82
employed AC signals with
controlled reverse current to < 10% to form coatings with superior corrosion resistance. Nold and
Clasen81
used asymmetric AC square wave with negative net DC component to deposit alumina
particles coatings from aqueous suspensions. The obtained coatings were smooth and bubble-
free. Yue et al.83
coupled a weak DC to a strong AC field to deposit Ag-sheathed Bi2Sr2CaCu2Oδ
tapes with improved microstructures.
The main characteristics of EPD under asymmetrical AC signals with net DC component are:
i) In order to prevent formation of bubbles, if the applied current density increased, the frequency
should also be increased.81
ii) Compared to pure DC, the obtained deposition rates are low, but the quality is better since the
coatings have no incorporated gas bubbles.
iii) If the employed AC field is stronger than the DC component, the produced microstructures
should have high probability of orientation,83
thus a better quality.
3.2.3. Asymmetrical AC field with no net DC component. Fig. 2E depicts an example of the
asymmetrical AC waveform with no net DC component. It will be noted that surface areas of the
positive and negative half-cycles are equal. Thus, theoretically, no net DC component is induced
(∫Edt = 0 over one period) to cause migration of the charged particle. Nevertheless, the difference
in potential height and time duration (E–t) between the two half-cycles could cause the particle to
migrate greater distance just like in DC fields, if the applied voltage is sufficiently high.
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (25 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
For low electric field strengths, traditional electrophoresis theory assumes a linear dependence
between the velocity of the particle motion, Veph, and the electric field strength, E, as illustrated in
eqn (1). If the voltage is sufficiently high, this theory becomes non-linear and can be described by
adding a second term with the cubic dependence on the electric field strength:20
Veph = μephE + μeph,3E3
(6)
In other words, in the signal of Fig. 2E, during the weak voltage-pulse, the nonlinear component
would be absent and only the linear one is present.
The theory of non-linear or non-uniform electrophoresis was observed and theoretically described
in many papers in the course of the past 35 years20,84–94
and the reason behind it is to do with the
electrical double layer of the suspended charged particle. Stotz86
suggested that if the electric
field is sufficiently strong, the electric double layer would completely be stripped off. Thus, the
particle charge can directly be calculated by equating the Coulomb and Stokes forces.
Recently, the theory of nonlinear electrophoresis was tested experimentally and found to
successfully produce thick deposits of inorganic,95,96
organic–inorganic particles97
and enzymes
and biological cells.24,28,29,98–100,103
Using asymmetrical triangular waves, Neirinck et al.95,96
deposited thick and uniform alumina coatings with higher green density from low aqueous
conductivity suspensions at 50 Hz and 500 Vp–p. Green density can be defined as the ratio of the
ceramic powder volume to the external volume of the deposit. If the green density is low,
cracking during drying and/or sintering of the deposit occur because of the large change in the
volume. Fig. 11 illustrates the shape of the triangular wave used for EPD and the resulting
alumina deposit in comparison with a coating obtained using CDC. While using CDC from
aqueous suspensions, a porous coating is formed; the deposit produced under asymmetrical AC
waveform is non-porous and homogenous. The reason for that is to do with water electrolysis.
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (26 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
Fig. 11 (A) One period of the applied asymmetric triangular AC
signal and alumina deposits formed using 100 V DC for 1200 s (B)
and 50 Hz and 500 Vp–p asymmetric AC field (C). Image
reproduced from ref. 95 with permission of Elsevier.
According to theoretical predictions, electrochemical reactions are suppressed using symmetric
AC signals (Fig. 2C) if the frequency is sufficiently high because most of the electrochemical
reactions are slow.20
Moreover, even when the frequency lies below the cut-off frequency of the
electrochemical reaction, reaction products formed during the positive (or negative) part of the
period are partly consumed when the signal is reversed during the rest of the period, thus
lowering the reaction products. By contrast, when asymmetrical AC signals such as the triangular
wave of Fig. 11 are used of which the integral over one period is zero, the difference in the
voltage height and time duration (E–t) between the positive and the negative half-cycles will
produce water electrolysis. The rate of electrolysis increases by lowering the frequency, elevating
the voltage and the ionic conductivity of the suspension.101
However, compared to the electrolysis
rates obtained by CDC, the rates under asymmetrical AC without net DC component are
significantly low to yield large gas bubbles and damage of the deposited coating.
It turns out that the conditions from which EPD is accomplished under asymmetrical AC without
net DC component including aqueous solvents and low electrolysis rates are conditions suitable
to deposit biomolecules such as enzymes and biological cells. Ammam and Fransaer24
demonstrated that using asymmetrical triangular waveform of Fig. 11, thick and active layers of
glucose oxidase (more than 10 μm) could be deposited at 30 Hz and 160 Vp–p. Such thicknesses
cannot be achieved by classical electrodeposition from either buffers27
or low conductivity
solutions.49
This suggests that under asymmetrical waves, the enzymes migrate greater distance to
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (27 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
reach the electrode and deposit. Also, 89 μm thick layers of biological cells, S. Cerevisiae, were
deposited under the applied conditions of 30 Hz and 200 Vp–p for 30 min (Fig. 12B). By
comparison, using symmetrical triangular AC waves without net DC component, only a
monolayer of S. Cerevisiae can be formed (Fig. 12A).
Fig. 12 SEM micrographs showing the morphology of deposited S.
Cerevisiae cells layers using symmetrical triangular waveform for
30 min at 30 Hz and 200 Vp–p (A) and using asymmetrical triangular
wave of Fig. 11(A) for 30 min at 30 Hz and 200 Vp–p (B). Part of
the image reproduced from ref. 28 with permission of Elsevier.
The main characteristics of EPD under asymmetrical AC waves without net DC component are:
i) The deposition yield increases linearly with the polarization time for both inorganic ceramic
materials95,96
and biochemical and biological species.24,28
ii) The deposition rates vary quasi-linearly with the applied amplitude then reach a saturation
plateau,24,95
confirming in some sort that nonlinear mode of electrophoresis takes place at high
voltages (eqn (6)).
iii) With respect to frequency, the deposition yield increases with the frequency from 0–50 Hz,
reaches a plateau95
then drops at elevated frequencies.24
This is understandable since if the
frequency is changing faster, the particles will no longer follow the AC field because of their
inertia. As a consequence, the particles oscillate in a single place and their net migration is
significantly reduced.
4. Applications of films by EPD under PDC and AC
In recent years, there has been a rising interest in nano and micro-structured materials because
they usually exhibit novel and improved properties suitable for various applications. Compared to
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (28 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
other deposition processes such as lithography, self-assembly, dip coating and spin coating, EPD
technique offers the advantage of being versatile, cost saving and more importantly, allows
deposition of high rates of particles in a controlled structural manner.
Although, applications of films by EPD under CDC fields are wide and can be found in advanced
ceramic materials, coatings for thin and thick films, multilayered composites, functionally graded
materials, hybrid materials, self-supported components, micro-patterned assemblies, and
nanotechnology.1
EPD under modulated electric fields, PDC and AC, offers new application
perspectives such as in biotechnology. Because EPD can be accomplished from aqueous
suspensions with low electrolysis rates under modulated electric fields, a variety of biochemical
and biological species can be deposited to yield highly active layers suitable for a range of
applications including biosensors, biofuel cells and bioreactors.24,28,29,75,98–104
Because EPD is an automated process, a variety of parameters such as voltage, frequency,
concentration of the dispersed species and deposition time can be controlled to yield a better
response under the optimized conditions. With regard to this, large number of biosensors with
improved characteristics have recently been designed and manufactured by means of EPD under
PDC and AC electric fields for detection of various analytes including glucose,24,49,99
lactose,98
glutamate100
and H2O2.103
Moreover, it is found that some biosensors are even dependable for
determination of the analyte in real samples such as in milk and in blood.98,99
The latter is
interesting considering the challenging aspects of the behavior of biosensors in real samples.105
By adding redox mediators, these electrodes have also been demonstrated to be useful for the
manufacturing of glucose/O2 biofuel cells.104
Various microorganisms such as E. coli and S. Serevisiae cells have also been successfully
deposited under modulated electric fields to form active monolayers29,75,102
and multilayers.28
In
addition, some studies demonstrated that the viability of the deposited cells is even superior with
respect to similarly treated free cells, thus improved bioreactors.28
Another important aspect of modulated electric fields over the classical CDC in EPD process is
the control over the orientation of the particle during the deposition. The latter yields better
ordered nano and micro-structures. In view of this, controlled zeolite microstructures can be
formed on glassy carbon under PDC44
and, under AC fields, rod-shaped bacteria A. naeslundii75
as well as Bi2Sr2CaCu2Oδ
tapes83
are observed to align parallel to the AC field. The well-
organized and oriented deposited structures give rise to improved properties which is observed in
many applications including superconductors,83
supercapacitors,97
field emission display devices
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (29 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
based carbon nanotubes48
and sensitive ceramic gas sensors for CO and NO2 detection.77–79
Because PDC and AC generate low rate of water electrolysis and prevent coalescence between
gas bubbles, high quality coatings useful for large range of applications such as ceramics and
polymers can be produced.41–47,71,72,80,81,95,96
The smooth and non-porous texture of the coatings
yields better anticorrosion properties.
5. Conclusions
The reviewed literature revealed that EPD under modulated electric fields, PDC and AC, is a very
promising process for the deposition of high quality coatings. From environmentally friendly
aqueous solvents, it is shown that a variety of materials including, inorganic, organic–inorganic
and biochemical and biological species can be deposited in controlled fashions. The formed
deposits displayed improved characteristics compared to what can be obtained by classical CDC
fields including smooth and bubble-free films, well oriented microstructures, and high activity
biochemical and biological deposited species. In addition, because EPD under PDC and AC is
automated, this leads to high reproducibility. The latter have been proven to lead to new
applications particularly in biotechnology such as in biosensors (glucose, glutamate, hydrogen
peroxide), biofuel cells and cell based bioreactors with improved characteristics. With respect to
this, particular attention should be paid to deposition of biochemical and biological charged
particles such as enzymes and biological cells because the conditions under which EPD can be
performed are now suitable for these species. Given the great potential of EPD under modulated
electric fields for manipulation and assembly of particles, further research and development of
these processes will allow the understanding of the mechanisms behind the assemblies. Also,
design and fabrication of 2D and 3D dimensional microstructures for novel generation of future
advanced applications in nano and biotechnology.
Acknowledgements
The author would like to thank KU Leuven (GOA/08/007) and the Belgian Federal Science
Policy Office (BELSPO) through the IUAP project INANOMAT (contract P6/17, Belgium) and
Natural Sciences and Engineering Research Council of Canada, and the University of Ontario
Institute of Technology (Canada) for their support.
References
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (30 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
1. L. Besra and M. Liu, A review on fundamentals and applications of electrophoretic
deposition (EPD), Prog. Mater. Sci., 2007, 52, 1–61 CrossRef CAS Search PubMed .
2. F. Begona and M. Rodrigo, EPD kinetics: A review , J. Eur. Ceram. Soc., 2010, 30, 1069–
1078 CrossRef Search PubMed .
3. I. Corni, M. P. Ryan and A. R. Boccaccini, Electrophoretic deposition: From traditional
ceramics to nanotechnology, J. Eur. Ceram. Soc., 2008, 28, 1353–
1367 CrossRef CAS Search PubMed .
4. O. Van der Biest and L. J. Vandeperre, Electrophoretic deposition of materials, Annu. Rev.
Mater. Sci., 1999, 29, 327–352 CrossRef CAS Search PubMed .
5. A. J. Bard, L. R. Faulkner, Electrochemical methods, Fundamentals and Applications,
Wiley, NY, 2nd edn, 2001 Search PubMed .
6. H. von Both and J. Hauβelt, Ceramic microstructures by electrophoretic deposition of
colloidal suspensions, in Proceedings on the electrophoretic deposition conference 2002,
ed. A. R. Boccaccini, O. Vanderbiest, P. S. Nicolson and J. Talbot, Electrochemical
Society Proceedings, 2002, vol. 21, pp. 78–85 Search PubMed .
7. M. S. Chronberg and F. Händle, Processes and equipment for the production of materials
by electrophoresis ELEPHANT, Interceram, 1978, 27, 33–34 Search PubMed .
8. A. V. Kerkar, R. W. Rice, R. M. Spotnitz, Manufacture of optical ferrules by
electrophoretic deposition, US Patent, 5 194 129 Search PubMed .
9. O. Sakurada, K. Suzuki, T. Miura and M. Hashiba, Bubble free electrophoretic deposition
of aqueous zirconia suspensions with hydroquinone, J. Mater. Sci., 2004, 39, 1845–
1847 CrossRef CAS Search PubMed .
10. S. Lebrette, C. Pagnoux and P. Abelard, Fabrication of titania dense layers by
electrophoretic deposition in aqueous media, J. Eur. Ceram. Soc., 2006, 26, 2727–
2734 CrossRef CAS Search PubMed .
11. R. Clasen, Forming of compacts of submicron silica particles by electrophoretic
deposition, in Proceedings of the 2nd Int. Conf. on Powder Processing Science, pp. 633–
640, Deutsche Keramische Gesellschaft, Berchtesgaden ed. H. Hausner, G. L. Messing
and S. Hirano, 1988, vol. 10, pp. 12–14 Search PubMed .
12. M. Ordung, J. Lehmann and G. Ziegler, Fabrication of fibre reinforced green bodies by
electrophoretic deposition of silicon powder from aqueous suspension, J. Mater. Sci.,
2004, 39, 889–894 CrossRef CAS Search PubMed .
13. J. Tabellion and R. Clasen, Electrophoretic deposition from aqueous suspensions for near-
shape manufacturing of advanced ceramics and glasses-applications, J. Mater. Sci., 2004,
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (31 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
39, 803–811 CrossRef CAS Search PubMed .
14. C. Oetzel and R. Clasen, Manufacturing of zirconia components by electrophoretic
deposition of nanosized powders, proceeding of the 27th Annual Cocoa Beach Conference
on Advanced Ceramics and Composites: A, ed. W. M. Kriven and H. T. Lin, Ceramic
Engineering and Science Proceedings, 2008, vol. 24, pp. 69–74 Search PubMed .
15. J. I. Hamagami, K. Kanamura, T. Umegaki, N. Fujiwara, M. Ito and S. Hirata, Direct
deposition of alumina particles onto nonconductive porous ceramics by electrophoresis, in
proceedings on the electrophoretic deposition conference 2002, ed. A. R. Boccaccini, O.
Vanderbiest, P. S. Nicolson and J. Talbot, Electrochemical Society Proceedings, 2002,
vol. 21, pp. 55–61 Search PubMed .
16. S. Novak, U. Maver, S. Peternel, P. Venturini, M. Bele and M. Gaberscek, Electrophoertic
deposition as a tool for separation of protein inclusion bodies from host bacteria in
suspension, Colloids Surf., A, 2009, 340, 155–160 CrossRef CAS Search PubMed .
17. P. Sarkar and P. S. Nicholson, Electrophoretic deposition (EPD): mechanisms, kinetics,
and application to ceramics, J. Am. Ceram. Soc., 1996, 79, 1987–
2002 CrossRef CAS Search PubMed .
18. J. Lyklema, Water at interfaces: a colloid-chemical approach, J. Colloid Interface Sci.,
1977, 58, 242–250 CrossRef CAS Search PubMed .
19. O. D. Velev and K. H. Bhatt, On-chip micromanipulation and assembly of colloids
particles by electric fields, Soft Matter, 2006, 2, 738–750 RSC .
20. A. S. Dukhin and S. S. Dukhin, Aperiodic capillary electrophoresis method using an
alternating current electric field for separation of macromolecules, Electrophoresis, 2005,
26, 2149–2153 CrossRef CAS Search PubMed .
21. M. H. Oddy and J. G. Santiago, A method for determining electrophoretic and
electroosmotic mobilities using AC and DC electric field, J. Colloid Interface Sci., 2004,
269, 192–204 CrossRef CAS Search PubMed .
22. M. Zarbov, I. Schuster, L. Gal-Or Methodology for selection of charging agents for
electrophoretic deposition of ceramic particles, in proceedings on the electrophoretic
deposition conference 2002, ed. A. R. Boccaccini, O. Vanderbiest, P. S. Nicolson and J.
Talbot, Electrochemical Society Proceedings, 2002, vol. 21, pp. 39–46 Search PubMed .
23. R. N. Basu, C. A. Randall and M. J. Mayo, Fabrication of dense zirconia electrolyte films
for tubular solid oxide fuel cells by electrophoretic deposition, J. Am. Ceram. Soc., 2001,
1, 33–40 CrossRef Search PubMed .
24. M. Ammam and J. Fransaer, AC-electrophoretic deposition of glucose oxidase, Biosens.
Bioelectron., 2009, 25, 191–197 CrossRef CAS Search PubMed .
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (32 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
25. J. Lyklema, H. P. Leeuwen and M. Minor, DLVO-theory, a dynamic re-interpretation,
Adv. Colloid Interface Sci., 1999, 83, 33–69 CrossRef CAS Search PubMed .
26. B. Ferrari and R. Moreno, The conductivity of aqueous Al2O3 slips for electrophoretic
deposition, Mater. Lett., 1996, 28, 353–355 CrossRef CAS Search PubMed .
27. N. Matsumoto, X. Chen and G. S. Wilson, Fundamental studies of glucose oxidase
deposition on a Pt electrode, Anal. Chem., 2002, 74, 362–367 CrossRef CAS Search PubMed
.
28. M. Ammam and J. Fransaer, Alternating current electrophoretic deposition of
Saccharomyces cerevisiae cells and the viability of the deposited biofilm in ethanol
production, Electrochim. Acta, 2010, 55, 3206–3212 CrossRef CAS Search PubMed .
29. B. Neirinck, L. Van Mellaert, J. Fransaer, O. Van der Biest, J. Anne and J. Vleugels,
Electrophoretic deposition of bacterial cells, Electrochem. Commun., 2009, 11, 1842–
1845 CrossRef CAS Search PubMed .
30. N. Heavens, Electrophoretic deposition as a processing route for ceramics, in Advanced
ceramic processing and technology, ed G. P. Binner, Noyes Publications, Park Ridge
(NJ), USA, 1990, vol.1, pp. 255–283 Search PubMed .
31. R. W. Powers, The electrophoretic forming of beta-alumina ceramic, J. Electrochem. Soc.,
1975, 122, 482–486 CrossRef Search PubMed .
32. Z. Jianling, W. Xiaohui and L. Longtu, Electrophoretic deposition of BaTiO3 films from
aqueous suspensions, Mater. Chem. Phys., 2006, 99, 350–353 CrossRef Search PubMed .
33. H. C. Hamaker and E. J. W. Verwey, The role of the forces between the particles in
electrodeposition and other phenomena, Trans. Faraday Soc., 1940, 35, 180–185 RSC
.
34. F. Grillon, D. Fayeulle and M. Jeandin, J. Mater. Sci. Lett., 1992, 11, 272–
275 CrossRef CAS Search PubMed .
35. H. Koelmans, Suspensions in Non-Aqueous Media, Phillips Res. Rep., 1995, 10, 161–
193 Search PubMed .
36. D. De and P. S. Nicholson, Role of ionic depletion in deposition during electrophoretic
deposition, , J. Am. Ceram. Soc., 1999, 8, 3031–3036 Search PubMed .
37. (a) W. D. Ristenpart, I. A. Aksay and D. A. Saville, Assembly of colloidal aggregates by
electrohydrodynamic flow: kinetic experiments and scaling analysis, , Phys. Rev., 2004,
E69, 0214051–0214058 Search PubMed ; (b) M. G. Song, K. J. M. Bishop, A. O.
Pinchuk, B. Kowalczyk and B. A. Grzybowski, Formation of dense nanoparticle
monolayer mediated by alternating current electric fields and electrohydrodynamic flows,
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (33 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
J. Phys. Chem. C, 2010, 114, 8800–8805 CrossRef CAS Search PubMed .
38. Y. Solomentsev, M. Bohmer and J. L. Anderson, Particle clustering and pattern formation
during electrophoretic deposition: A hydrodynamic model, Langmuir, 1997, 13, 6058–
6068 CrossRef CAS Search PubMed .
39. S. Ghosal, Fluid mechanics of electroosmotic flow and its effect on band broadening in
capillary electrophoresis, Electrophoresis, 2004, 25, 214–228 CrossRef CAS Search PubMed
.
40. D. C. Prieve, P. J. Sides and C. L. Wirth, 2D particle assembly of colloidal particles on a
planar electrode, Curr. Opin. Colloid Interface Sci., 2010, 15, 160–
174 CrossRef CAS Search PubMed .
41. L. Besra, T. Uchikoshi, T. S. Suzuki and Y. Sakka, Pulsed-DC electrophoretic deposition
(EPD) of aqueous alumina suspension for controlling bubble incorporation and deposit
microstructure, Key Eng. Mater., 2009, 412, 39–44 CrossRef CAS Search PubMed .
42. L. Besra, T. Uchikoshi, T. S. Suzuki and Y. Sakka, Application of constant current pulse
to suppress bubble incorporation and control deposit morphology during aqueous
electrophoretic deposition (EPD), J. Eur. Ceram. Soc., 2009, 29, 1837–
1845 CrossRef CAS Search PubMed .
43. N. N. Naim, M. Kuwata, H. Kamiya and I. W. Lenggoro, Deposition of TiO2,
nanoparticles in surfactant-containing aqueous suspension by a pulsed DC charging-mode
electrophoresis, J. Ceram. Soc. Jpn., 2009, 117, 127–132 CrossRef Search PubMed .
44. B. Yu and S. B. Khoo, Controllable zeolite films on electrodes-comparing dc voltage
electrophoretic deposition and a novel pulsed voltage method, Electrochem. Commun.,
2002, 4, 737–742 CrossRef CAS Search PubMed .
45. N. M. Nazli, I. Motoyuki, K. Hidehiro and L. I. Wuled, Electrophoretic packing structure
from aqueous nanoparticles suspension in pulse DC charging, Colloids and Surfaces,
Colloids Surf., A, 2010, 360, 13–19 CrossRef Search PubMed .
46. L. Besra, T. Uchikoshi, T. S. Suzuki and Y. Sakka, Experimental verification of pH
localization mechanism of particle consolidation at the electrode/solution interface and its
application to pulsed DC electrophoretic deposition, J. Eur. Ceram. Soc., 2010, 30, 1187–
1193 CrossRef CAS Search PubMed .
47. M. N. Naim, M. Lijima, K. Sasaki, M. Kuwata and H. Kamiya, Electrical-driven
disaggregation of the two-dimensional assembly of colloidal polymer particles under pulse
DC charging, Adv. Powder Technol., 2010, 21, 534–541 CrossRef CAS Search PubMed .
48. C. Y. Hsiao, T. F. Chan, S. H. Lee, K. Cheng, Y. A. Li, L. J. Tsai, J. S. Fang and C. C.
Kuo, Electrophoresis deposition method to fabricate CNT-FED cathode in water base
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (34 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
solution, Dig. Tech. Pap. - Soc. Inf. Disp. Int. Symp., 2005, 36, 411–
413 CrossRef CAS Search PubMed .
49. M. Ammam and J. Fransaer, A study on electrodeposition of glucose oxidase from low
conductivity solutions, Electrochim. Acta, 2010, 55, 9125–
9131 CrossRef CAS Search PubMed .
50. P. J. Sides and C. W. Tobias, A close view of gas evolution from the back side of a
transparent electrode, J. Electrochem. Soc., 1985, 132, 583–
587 CrossRef CAS Search PubMed .
51. M. Ammam and J. Fransaer, Micro-biofuel cell powered by glucose/O2 based on electro-
deposition of enzyme, conducting polymer and redox mediators: Preparation,
characterization and performance in human serum, Biosens. Bioelectron., 2010, 25, 1474–
1480 CrossRef CAS Search PubMed .
52. N. G. Green, A. Ramos and H. Morgan, AC electrokinetics: A survey of sub-micrometre
particle dynamics, J. Phys. D: Appl. Phys., 2000, 33, 632–641 CrossRef CAS Search PubMed
.
53. J. A. Fagan, P. J. Sides and D. C. Prieve, Evidence of multiple electrohydrodynamic
forces acting on a colloidal particles near an electrode due to an alternating current electric
field, Langmuir, 2005, 21, 1784–1794 CrossRef CAS Search PubMed .
54. P. J. Sides, Electrohydrodynamic particles aggregation on an electrode driven by an
alternating current electric field normal to it, Langmuir, 2001, 17, 5791–
5800 CrossRef CAS Search PubMed .
55. J. Kim, J. L. Anderson, S. Garoof and P. J. Sides, Effects of zeta potential and electrolyte
on particle interaction on an electrode under AC polarization, Langmuir, 2002, 18, 5387–
5391 CrossRef CAS Search PubMed .
56. J. A. Fagan, P. J. Sides and D. C. Prieve, Vertical motion of a charged colloids particles
near an AC polarized electrode with nonuniform potential distribution: Theory and
experimental evidence, Langmuir, 2004, 20, 4823–4834 CrossRef CAS Search PubMed .
57. J. A. Fagan, P. J. sides and D. C. Prieve, Mechanism of rectified lateral motion of particles
near electrodes in alternating electric fields below 1 kHz, Langmuir, 2006, 22, 9846–
9852 CrossRef CAS Search PubMed .
58. P. C. Y. Chen, Alternating current electrophoresis of human red blood cells, Ann. Biomed.
Eng., 1980, 8, 253–269 CrossRef CAS Search PubMed .
59. B. K. Gale and M. Srinivas, Cyclical electrical field flow fraction, Electrophoresis, 2005,
26, 1623–1632 CrossRef CAS Search PubMed .
60. Z. R. Li, G. R. Liu, J. Han, Y. Z. Chen, J. S. Wang and N. G. Hadjiconstantinou,
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (35 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
Transport of biomolecules in asymmetric nanofilter arrays, Anal. Bioanal. Chem., 2009,
394, 427–435 CrossRef CAS Search PubMed .
61. P. D. Grossman, J. C. Colburn, Capillary Electrophoresis: Theory and Practice,
Academic Press, New York, 1992 Search PubMed .
62. W. B. Russel, D. A. Saville, W. R. Schowalter, Colloidal Dispersions, Cambridge
University Press, 1995 Search PubMed .
63. P. F. Rider and R. W. O'Brien, The dynamic mobility of particles in a nondilute
suspension, J. Fluid Mech., 1993, 257, 607–636 CrossRef CAS Search PubMed .
64. H. A. Pohl, The motion and precipitation of suspensions in divergent electric fields, J.
Appl. Phys., 1951, 22, 869–871 CrossRef CAS Search PubMed .
65. H. A. Pohl, Dielectrophoresis, Cambridge University Press, 1978 Search PubMed .
66. T. B. Jones, Electromechanics of Particles, Cambridge University Press, New York,
1995 Search PubMed .
67. R. Pethig, Dielectrophoresis: Using inhomogeneous AC electrical fields to separate and
manipulate cells , Crit. Rev. Biotechnol., 1996, 16, 331–348 CrossRef Search PubMed .
68. W. M. Arnold, H. P. Schwan and U. Zimmermann, Surface conductance and other
properties of latex particles measured by electrorotation, J. Phys. Chem., 1987, 91, 5093–
5098 CrossRef CAS Search PubMed .
69. X. B. Wang, R. Pethig and T. B. Jones, Relationship of dielectrophoretic and
electrorotational behavior exhibited by polarized particles, J. Phys. D: Appl. Phys., 1992,
25, 905–912 CrossRef CAS Search PubMed .
70. R. Hagedorn, G. Fuhr, T. Muller and J. Gimsa, Traveling wave dielectrophoresis of
microparticles, Electrophoresis, 1992, 13, 49–54 CrossRef CAS Search PubMed .
71. (a) Making Rubber Objects From Dispersions by Electrophoretic Deposition in an
Alternating Current, Dunlop Rubber Co. Ltd. and The Anode Rubber Co. Ltd.,1930, DE
587700 19331107 Search PubMed ; (b) Goodlass Wall and Co LTD., Electrophoretic
deposition of resinous films on metallic objects, FR Pat, 1 409 893, 1969 Search PubMed
; (c) T. Sunamori, S. Obana, Electrophoretic Coating Process Using Alternating
Current, JP 51123243 A 19761027 Search PubMed ; (d) T. Sunamori, S. Obana,
Electrophoretic Coating of Substrates by Alternating Currents, 1976, JP 51055340 A
19760515 Search PubMed ; (e) T. Sunamori, Y. Obana, Alternating Current
Electrophoretic Coating of Metal with Resins, 1976, JP 51086544 A
19760729 Search PubMed ; (f) T. K. Kokai, Electrophoretic Coating of Anodized
Aluminum Substrates by Alternating Current, 1980, JP 55054596 A
19800421 Search PubMed .
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (36 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
72. R. Riahifar, B. Raissi, E. Marzbanrad and C. Zamani, Effects of parameters on deposition
pattern of ceramic nanoparticles in non-unifrom AC electric field, J. Mater. Sci.: Mater.
Electron., 2011, 22, 40–46 CrossRef CAS Search PubMed .
73. Z. R. Ul'berg, T. V. Kuznetsova and A. S. Dukhin, Electrophoretic dispersion deposition
in external alternating electric field, Dopov. Akad. Nauk Ukr. RSR, Ser. B: Geol., Khim.
Biol. Nauki, 1979, 11, 936–940 Search PubMed .
74. Y. Hirata, A. Nishimoto and Y. Ishihara, Forming of alumina powder by electrophoretic
deposition, J. Ceram. Soc. Jpn., 1991, 99, 108–113 CrossRef CAS Search PubMed .
75. A. T. Poortinga, R. Bos and H. J. Busscher, Controlled electrophoresis deposition of
bacteria to surface for the design of biofilms, Biotechnol. Bioeng., 2000, 67, 117–
120 CrossRef CAS Search PubMed .
76. A. R. Gardeshzadeh, B. Raissi and E. Marzbanrad, Deposition of multiwall carbon
nanotubes using low frequency alternating electrophoretic deposition, Key Eng. Mater.,
2009, 412, 83–86 CrossRef CAS Search PubMed .
77. A. R. Gardeshzadeh, B. Raissi, E. Marzbanrad and H. Mohebbi, Fabrication of resistive
CO gas sensor based on SnO2 nanopowders via low frequency AC electrophoretic
deposition, J. Mater. Sci.: Mater. Electron., 2009, 20, 127–131 CrossRef CAS Search PubMed
.
78. E. K. Heidari, C. Zamani, E. Marzbanrad, B. Raissi and S. Nazarpour, WO3-based NO2
sensors fabricated through low frequency AC electrophoretic deposition, Sens. Actuators,
B, 2010, B146, 165–170 CrossRef CAS Search PubMed .
79. E. K. Heidari, E. Marzbanrad, C. Zamani and B. Raissi, Nanocasting synthesis of ultrafine
WO3 nanoparticles for gas sensing applications, Nanoscale Res. Lett., 2010, 5, 370–
373 CrossRef CAS Search PubMed .
80. R. Riahifar, E. Maezbanrad, B. R. Dehkordi and C. Zamani, Role of substrate potential on
filling the gap between two planar parralel electrodes in electrophoretic deposition, Mater.
Lett., 2010, 64, 559–561 CrossRef CAS Search PubMed .
81. A. Nold and R. Clasen, Bubbles free electrophoretic deposition shaping from aqueous
suspension with micro point electrode, J. Eur. Ceram. Soc., 2010, 30, 2971–
2975 CrossRef CAS Search PubMed .
82. Y. Shindo, M. Nakamura and T. Tanaka, Alternating current electrophoretic coating
process. III. Effect of substrate metals on the properties of coatings, Aruminyumu Hyomen
Shori Kenkyu Chosa Hokoku, 1974, 91, 73–74 CAS Search PubMed .
83. C. F. J. Yue, D. Kumar and R. K. Singh, Fabrication of Ag-sheathed Bi-Sr-Ca-Cu-O thick
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (37 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
films by a novel AC electric field assisted electrophoretic deposition method, Phys. C,
1999, 314, 291–298 CrossRef CAS Search PubMed .
84. S. S. Dukhin, A. K. Vidybida, A. S. Dukhin and A. A. Serikov, Aperiodic electrophoresis.
Directed drift of disperse particles in a uniform, alternating anharmonic electric field,
Kolloidn. Zh., 1988, 49, 853–857 Search PubMed .
85. S. S. Dukhin, B. V. Derjaguin, Electrophoresis, 1972, ch. 10, Nauka, Moscow, pp. 195–
213 Search PubMed .
86. S. Stotz, Field dependence of the electrophoretic mobility of particles suspended in low-
conductivity liquids , J. Colloid Interface Sci., 1978, 65, 118–
130 CrossRef CAS Search PubMed .
87. S. S. Dukhin, T. S. Simonova and I. T. Gorbachuk, Physics of solid body, Bull. Kiev
Pedagogical Institute, 1972, 113–123 Search PubMed .
88. P. S. Vincett, High-field electrophoresis of insulating particles in insulating liquids. I. An
electrical transient technique for studying particle mobility, charge, degree of aggregation,
adhesive forces, and high-field charging mechanisms, J. Colloid Interface Sci., 1980, 76,
83–94 CrossRef CAS Search PubMed .
89. P. S. Vincett, High-field electrophoresis of insulating particles in insulating liquids. II. A
study of the basic transport mechanisms, including a novel space charge limited
conduction process, J. Colloid Interface Sci., 1980, 76, 95–106 CrossRef CAS Search PubMed
.
90. S. S. Dukhin, Electrophoresis at large peclet numbers, Adv. Colloid Interface Sci., 1991,
36, 219–248 CrossRef CAS Search PubMed .
91. N. A. Mishchuk and S. S. Dukhin, Electrophoresis of solid particles at large Peclet
numbers, Electrophoresis, 2002, 23, 2012–2022 CrossRef CAS Search PubMed .
92. S. S. Dukhin, Electrokinetic phenomena of the second kind and their applications, Adv.
Colloid Interface Sci., 1991, 35, 173–196 CrossRef CAS Search PubMed .
93. N. A. Mishchuk, S. S. Dukhin, in Interfacial Electrokinetics and Electrophoresis, ed. A.
Delgado, Marcel Decker, New York/Basel, 2002, pp. 241–275 Search PubMed .
94. A. S. Dukhin, Biospecific mechanism of double layer formation and peculiarities of cell
electrophoresis , Colloids Surf., A, 1993, 73, 29–48 CrossRef Search PubMed .
95. B. Neirinck, J. Fransaer, O. Van der Biest and J. Vleugels, Aqueous electrophoretic
deposition in asymmetric AC electric fields (AC-EPD), Electrochem. Commun., 2009, 11,
57–60 CrossRef CAS Search PubMed .
96. B. Neirinck, J. Fransaer, J. Vleugels and O. Van der Biest, Aqueous Electrophoretic
Deposition at High Electric Fields, Electrophoretic deposition: Fundamentals and
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (38 de 39) [31/01/2014 02:10:17 p.m.]
Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H
applications III Book Series: Key Eng. Mater., 2009, vol. 412, pp. 33–38 Search PubMed .
97. M. Ammam and J. Fransaer, Ionic liquid-heteropolyacid: Synthesis, characterization, and
supercapacitor study of films deposited by electrophoresis, J. Electrochem. Soc., 2010,
158, A14–A21 CrossRef Search PubMed .
98. M. Ammam and J. Fransaer, Two-enzyme lactose biosensor based on β-galactosidase and
glucose oxidase deposited by AC-electrophoresis: Characteristics and performance for
lactose determination in milk, Sens. Actuators, B, 2010, B148, 583–
589 CrossRef CAS Search PubMed .
99. M. Ammam and J. Fransaer, Glucose microbiosensor based on glucose oxidase
immobilized by AC-EPD: Characteristics and performance in human serum and in blood
of critically ill rabbits, Sens. Actuators, B, 2010, B145, 46–53 CrossRef CAS Search PubMed
.
100. M. Ammam and J. Fransaer, Highly sensitive and selective glutamate microbiosensor
based on cast polyurethane/AC-electrophoresis deposited multiwalled carbon nanotubes
and then glutamate oxidase/electrosynthesized polypyrrole/Pt electrode, Biosens.
Bioelectron., 2010, 25, 1597–1602 CrossRef CAS Search PubMed .
101. M. Ammam and J. Fransaer, Effects of AC-electrolysis on the enzymatic activity of
glucose oxidase, Electroanalysis, 2011, 23, 755–763 CrossRef CAS Search PubMed .
102. V. Brisson and R. D. Tilton, Self-assembly and two-dimensional patterning of cell arrays
by electrophoretic deposition, Biotechnol. Bioeng., 2002, 77, 290–
295 CrossRef CAS Search PubMed .
103. M. Ammam and J. Fransaer, AC-electrophoretic deposition of metalloenzymes: Catalase
as a case study for the sensitive and selective detection of H2O2, Sens. Actuators, B, 2011,
160, 1063–1069 CrossRef CAS Search PubMed .
104. . M. Ammam and J. Fransaer, Glucose/O2 biofuel cell based on enzymes, redox mediators,
and Multiple-walled carbon nanotubes deposited by AC-electrophoresis then stabilized by
electropolymerized polypyrrole, Biotechnol. Bioeng., 2012, 109, 1601, DOI:10.1002/bit.24438
.
105. G. S. Wilson and M. Ammam, In vivo Biosensors, FEBS J., 2007, 274, 5452–
546 CrossRef CAS Search PubMed .
This journal is © The Royal Society of Chemistry 2012
http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (39 de 39) [31/01/2014 02:10:17 p.m.]

More Related Content

What's hot

Ap3193100
Ap3193100Ap3193100
Ap3193100IJMER
 
TREATING WASTE WATER USING ELECTROCOAGULATION APPROACH
TREATING WASTE WATER USING ELECTROCOAGULATION APPROACHTREATING WASTE WATER USING ELECTROCOAGULATION APPROACH
TREATING WASTE WATER USING ELECTROCOAGULATION APPROACHIAEME Publication
 
Fuel Cell Vehicles
Fuel Cell VehiclesFuel Cell Vehicles
Fuel Cell Vehiclesguestc4c2a3
 
Recent progress in non platinum counter electrode materials for dye sensitize...
Recent progress in non platinum counter electrode materials for dye sensitize...Recent progress in non platinum counter electrode materials for dye sensitize...
Recent progress in non platinum counter electrode materials for dye sensitize...Science Padayatchi
 
Synopsis : Bismuth Sodium Titanate ( A lead free Ferroelectric Material
Synopsis : Bismuth Sodium Titanate ( A lead free Ferroelectric MaterialSynopsis : Bismuth Sodium Titanate ( A lead free Ferroelectric Material
Synopsis : Bismuth Sodium Titanate ( A lead free Ferroelectric MaterialNational Tsing Hua University
 
Solar hydrogen generation
Solar hydrogen generationSolar hydrogen generation
Solar hydrogen generationsbit
 
Lithium Batteries and Supercapacitors
Lithium Batteries and SupercapacitorsLithium Batteries and Supercapacitors
Lithium Batteries and SupercapacitorsBing Hsieh
 
Photoelectrochemical splitting of water for hydrogen generation: Basics & Fut...
Photoelectrochemical splitting of water for hydrogen generation: Basics & Fut...Photoelectrochemical splitting of water for hydrogen generation: Basics & Fut...
Photoelectrochemical splitting of water for hydrogen generation: Basics & Fut...RunjhunDutta
 
Sunlight-driven water-splitting using two-dimensional carbon based semiconduc...
Sunlight-driven water-splitting using two-dimensional carbon based semiconduc...Sunlight-driven water-splitting using two-dimensional carbon based semiconduc...
Sunlight-driven water-splitting using two-dimensional carbon based semiconduc...Pawan Kumar
 
Introduction to Photoelectrochemical (PEC) Water Splitting
Introduction to Photoelectrochemical (PEC) Water SplittingIntroduction to Photoelectrochemical (PEC) Water Splitting
Introduction to Photoelectrochemical (PEC) Water SplittingAnamika Banerjee
 
Organic Field Effect Transistor
Organic Field Effect TransistorOrganic Field Effect Transistor
Organic Field Effect Transistorsantosh meena
 
Final_Science_Display
Final_Science_DisplayFinal_Science_Display
Final_Science_DisplayBhavin Shah
 
Organic transistors
Organic transistorsOrganic transistors
Organic transistorsDeiptii Das
 
Rechargeable Sodium-ion Battery - The Future of Battery Development
Rechargeable Sodium-ion Battery - The Future of Battery DevelopmentRechargeable Sodium-ion Battery - The Future of Battery Development
Rechargeable Sodium-ion Battery - The Future of Battery DevelopmentDESH D YADAV
 

What's hot (20)

Plastic Electronics
Plastic ElectronicsPlastic Electronics
Plastic Electronics
 
Ap3193100
Ap3193100Ap3193100
Ap3193100
 
TREATING WASTE WATER USING ELECTROCOAGULATION APPROACH
TREATING WASTE WATER USING ELECTROCOAGULATION APPROACHTREATING WASTE WATER USING ELECTROCOAGULATION APPROACH
TREATING WASTE WATER USING ELECTROCOAGULATION APPROACH
 
Fuel Cell Vehicles
Fuel Cell VehiclesFuel Cell Vehicles
Fuel Cell Vehicles
 
Recent progress in non platinum counter electrode materials for dye sensitize...
Recent progress in non platinum counter electrode materials for dye sensitize...Recent progress in non platinum counter electrode materials for dye sensitize...
Recent progress in non platinum counter electrode materials for dye sensitize...
 
Plastic electronics
Plastic electronicsPlastic electronics
Plastic electronics
 
Hybrid inorganic/organic semiconductor structures for opto-electronics.
Hybrid inorganic/organic semiconductor structures for opto-electronics.Hybrid inorganic/organic semiconductor structures for opto-electronics.
Hybrid inorganic/organic semiconductor structures for opto-electronics.
 
Synopsis : Bismuth Sodium Titanate ( A lead free Ferroelectric Material
Synopsis : Bismuth Sodium Titanate ( A lead free Ferroelectric MaterialSynopsis : Bismuth Sodium Titanate ( A lead free Ferroelectric Material
Synopsis : Bismuth Sodium Titanate ( A lead free Ferroelectric Material
 
Solar hydrogen generation
Solar hydrogen generationSolar hydrogen generation
Solar hydrogen generation
 
Lithium Batteries and Supercapacitors
Lithium Batteries and SupercapacitorsLithium Batteries and Supercapacitors
Lithium Batteries and Supercapacitors
 
Photoelectrochemical splitting of water for hydrogen generation: Basics & Fut...
Photoelectrochemical splitting of water for hydrogen generation: Basics & Fut...Photoelectrochemical splitting of water for hydrogen generation: Basics & Fut...
Photoelectrochemical splitting of water for hydrogen generation: Basics & Fut...
 
Sunlight-driven water-splitting using two-dimensional carbon based semiconduc...
Sunlight-driven water-splitting using two-dimensional carbon based semiconduc...Sunlight-driven water-splitting using two-dimensional carbon based semiconduc...
Sunlight-driven water-splitting using two-dimensional carbon based semiconduc...
 
Introduction to Photoelectrochemical (PEC) Water Splitting
Introduction to Photoelectrochemical (PEC) Water SplittingIntroduction to Photoelectrochemical (PEC) Water Splitting
Introduction to Photoelectrochemical (PEC) Water Splitting
 
Organic Field Effect Transistor
Organic Field Effect TransistorOrganic Field Effect Transistor
Organic Field Effect Transistor
 
Final_Science_Display
Final_Science_DisplayFinal_Science_Display
Final_Science_Display
 
Organic transistors
Organic transistorsOrganic transistors
Organic transistors
 
Electrosynthesis ecc2013
Electrosynthesis ecc2013Electrosynthesis ecc2013
Electrosynthesis ecc2013
 
Electrochemistry
Electrochemistry Electrochemistry
Electrochemistry
 
Rechargeable Sodium-ion Battery - The Future of Battery Development
Rechargeable Sodium-ion Battery - The Future of Battery DevelopmentRechargeable Sodium-ion Battery - The Future of Battery Development
Rechargeable Sodium-ion Battery - The Future of Battery Development
 
Slide radhi
Slide radhiSlide radhi
Slide radhi
 

Viewers also liked

Ciconf 2012 - Better than Ad-hoc
Ciconf 2012 - Better than Ad-hocCiconf 2012 - Better than Ad-hoc
Ciconf 2012 - Better than Ad-hocCalvin Froedge
 
Latso dan materi pengukuran dan suhu
Latso dan materi pengukuran dan suhuLatso dan materi pengukuran dan suhu
Latso dan materi pengukuran dan suhuari sudibjo
 
Ceramic films using cathodic electrodeposition
Ceramic films using cathodic electrodepositionCeramic films using cathodic electrodeposition
Ceramic films using cathodic electrodepositionMario ML
 
Freshman class meeting!
Freshman class meeting!Freshman class meeting!
Freshman class meeting!rwaxham
 
Career marketing-3.0-changing-the-way-career-services-representatives-market-...
Career marketing-3.0-changing-the-way-career-services-representatives-market-...Career marketing-3.0-changing-the-way-career-services-representatives-market-...
Career marketing-3.0-changing-the-way-career-services-representatives-market-...Robert Starks Jr
 
Robert starks-jr-does-your-career-center-speak-hashtag-career-services-traini...
Robert starks-jr-does-your-career-center-speak-hashtag-career-services-traini...Robert starks-jr-does-your-career-center-speak-hashtag-career-services-traini...
Robert starks-jr-does-your-career-center-speak-hashtag-career-services-traini...Robert Starks Jr
 
Materi listrik statis
Materi listrik statisMateri listrik statis
Materi listrik statisari sudibjo
 
Boston Code Dojo - Docker meetup slides
Boston Code Dojo - Docker meetup slidesBoston Code Dojo - Docker meetup slides
Boston Code Dojo - Docker meetup slidesCalvin Froedge
 

Viewers also liked (10)

Web Bots - CTF Game
Web Bots - CTF GameWeb Bots - CTF Game
Web Bots - CTF Game
 
Ciconf 2012 - Better than Ad-hoc
Ciconf 2012 - Better than Ad-hocCiconf 2012 - Better than Ad-hoc
Ciconf 2012 - Better than Ad-hoc
 
titanic books.docx
titanic books.docxtitanic books.docx
titanic books.docx
 
Latso dan materi pengukuran dan suhu
Latso dan materi pengukuran dan suhuLatso dan materi pengukuran dan suhu
Latso dan materi pengukuran dan suhu
 
Ceramic films using cathodic electrodeposition
Ceramic films using cathodic electrodepositionCeramic films using cathodic electrodeposition
Ceramic films using cathodic electrodeposition
 
Freshman class meeting!
Freshman class meeting!Freshman class meeting!
Freshman class meeting!
 
Career marketing-3.0-changing-the-way-career-services-representatives-market-...
Career marketing-3.0-changing-the-way-career-services-representatives-market-...Career marketing-3.0-changing-the-way-career-services-representatives-market-...
Career marketing-3.0-changing-the-way-career-services-representatives-market-...
 
Robert starks-jr-does-your-career-center-speak-hashtag-career-services-traini...
Robert starks-jr-does-your-career-center-speak-hashtag-career-services-traini...Robert starks-jr-does-your-career-center-speak-hashtag-career-services-traini...
Robert starks-jr-does-your-career-center-speak-hashtag-career-services-traini...
 
Materi listrik statis
Materi listrik statisMateri listrik statis
Materi listrik statis
 
Boston Code Dojo - Docker meetup slides
Boston Code Dojo - Docker meetup slidesBoston Code Dojo - Docker meetup slides
Boston Code Dojo - Docker meetup slides
 

Similar to Depositacion electroforetica dentro de campos electricos modulados

Electrochemical study of anatase TiO2 in aqueous sodium-ion electrolytes
Electrochemical study of anatase TiO2 in aqueous sodium-ion electrolytesElectrochemical study of anatase TiO2 in aqueous sodium-ion electrolytes
Electrochemical study of anatase TiO2 in aqueous sodium-ion electrolytesRatnakaram Venkata Nadh
 
Electro-Disinfection of Municipal Wastewater: Laboratory Scale Comparison bet...
Electro-Disinfection of Municipal Wastewater: Laboratory Scale Comparison bet...Electro-Disinfection of Municipal Wastewater: Laboratory Scale Comparison bet...
Electro-Disinfection of Municipal Wastewater: Laboratory Scale Comparison bet...IJERA Editor
 
Walker Electrochemical Paper
Walker Electrochemical PaperWalker Electrochemical Paper
Walker Electrochemical PaperPatrick Walker
 
Effect of morphology on the photoelectrochemical performance of nanostructure...
Effect of morphology on the photoelectrochemical performance of nanostructure...Effect of morphology on the photoelectrochemical performance of nanostructure...
Effect of morphology on the photoelectrochemical performance of nanostructure...Pawan Kumar
 
10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...
10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...
10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...Mahdi Robat Sarpoushi
 
Band edge engineering of composite photoanodes for dye sensitized solar cells
Band edge engineering of composite photoanodes for dye sensitized solar cellsBand edge engineering of composite photoanodes for dye sensitized solar cells
Band edge engineering of composite photoanodes for dye sensitized solar cellsvenkatamanthina
 
Zr doped TiO2 nanocomposites for dye sensitized solar cells
Zr doped TiO2 nanocomposites for dye sensitized solar cellsZr doped TiO2 nanocomposites for dye sensitized solar cells
Zr doped TiO2 nanocomposites for dye sensitized solar cellsvenkatamanthina
 
Chemistry and physics of dssc ppt
Chemistry and physics of dssc pptChemistry and physics of dssc ppt
Chemistry and physics of dssc pptN.MANI KANDAN
 
electrical-polarization-process (1).pdf
electrical-polarization-process (1).pdfelectrical-polarization-process (1).pdf
electrical-polarization-process (1).pdfDaniel Donatelli
 
electrical-polarization-process.pdf
electrical-polarization-process.pdfelectrical-polarization-process.pdf
electrical-polarization-process.pdfDaniel Donatelli
 
Recent advancements in tuning the electronic structures of transitional metal...
Recent advancements in tuning the electronic structures of transitional metal...Recent advancements in tuning the electronic structures of transitional metal...
Recent advancements in tuning the electronic structures of transitional metal...Pawan Kumar
 
Semiconductor part-2
Semiconductor part-2Semiconductor part-2
Semiconductor part-2Santanu Paria
 
Iaetsd dye sensitized solar cell
Iaetsd dye sensitized solar cellIaetsd dye sensitized solar cell
Iaetsd dye sensitized solar cellIaetsd Iaetsd
 
ZnO-TiO2 nanocomposite core-shell
ZnO-TiO2 nanocomposite core-shellZnO-TiO2 nanocomposite core-shell
ZnO-TiO2 nanocomposite core-shellvenkatamanthina
 
An introduction to electrocoagulation
An introduction to electrocoagulationAn introduction to electrocoagulation
An introduction to electrocoagulationChristos Charisiadis
 

Similar to Depositacion electroforetica dentro de campos electricos modulados (20)

final ppt on 30 sep 2022.pptx
final ppt on 30 sep 2022.pptxfinal ppt on 30 sep 2022.pptx
final ppt on 30 sep 2022.pptx
 
Electrochemical study of anatase TiO2 in aqueous sodium-ion electrolytes
Electrochemical study of anatase TiO2 in aqueous sodium-ion electrolytesElectrochemical study of anatase TiO2 in aqueous sodium-ion electrolytes
Electrochemical study of anatase TiO2 in aqueous sodium-ion electrolytes
 
20320140501001
2032014050100120320140501001
20320140501001
 
Electro-Disinfection of Municipal Wastewater: Laboratory Scale Comparison bet...
Electro-Disinfection of Municipal Wastewater: Laboratory Scale Comparison bet...Electro-Disinfection of Municipal Wastewater: Laboratory Scale Comparison bet...
Electro-Disinfection of Municipal Wastewater: Laboratory Scale Comparison bet...
 
Walker Electrochemical Paper
Walker Electrochemical PaperWalker Electrochemical Paper
Walker Electrochemical Paper
 
Effect of morphology on the photoelectrochemical performance of nanostructure...
Effect of morphology on the photoelectrochemical performance of nanostructure...Effect of morphology on the photoelectrochemical performance of nanostructure...
Effect of morphology on the photoelectrochemical performance of nanostructure...
 
10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...
10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...
10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...
 
Band edge engineering of composite photoanodes for dye sensitized solar cells
Band edge engineering of composite photoanodes for dye sensitized solar cellsBand edge engineering of composite photoanodes for dye sensitized solar cells
Band edge engineering of composite photoanodes for dye sensitized solar cells
 
Zr doped TiO2 nanocomposites for dye sensitized solar cells
Zr doped TiO2 nanocomposites for dye sensitized solar cellsZr doped TiO2 nanocomposites for dye sensitized solar cells
Zr doped TiO2 nanocomposites for dye sensitized solar cells
 
shang2010.pdf
shang2010.pdfshang2010.pdf
shang2010.pdf
 
shang2010.pdf
shang2010.pdfshang2010.pdf
shang2010.pdf
 
Chemistry and physics of dssc ppt
Chemistry and physics of dssc pptChemistry and physics of dssc ppt
Chemistry and physics of dssc ppt
 
electrical-polarization-process (1).pdf
electrical-polarization-process (1).pdfelectrical-polarization-process (1).pdf
electrical-polarization-process (1).pdf
 
electrical-polarization-process.pdf
electrical-polarization-process.pdfelectrical-polarization-process.pdf
electrical-polarization-process.pdf
 
Recent advancements in tuning the electronic structures of transitional metal...
Recent advancements in tuning the electronic structures of transitional metal...Recent advancements in tuning the electronic structures of transitional metal...
Recent advancements in tuning the electronic structures of transitional metal...
 
Hydrogen energy
Hydrogen energyHydrogen energy
Hydrogen energy
 
Semiconductor part-2
Semiconductor part-2Semiconductor part-2
Semiconductor part-2
 
Iaetsd dye sensitized solar cell
Iaetsd dye sensitized solar cellIaetsd dye sensitized solar cell
Iaetsd dye sensitized solar cell
 
ZnO-TiO2 nanocomposite core-shell
ZnO-TiO2 nanocomposite core-shellZnO-TiO2 nanocomposite core-shell
ZnO-TiO2 nanocomposite core-shell
 
An introduction to electrocoagulation
An introduction to electrocoagulationAn introduction to electrocoagulation
An introduction to electrocoagulation
 

Recently uploaded

Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.raviapr7
 
Quality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICEQuality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICESayali Powar
 
How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17Celine George
 
Clinical Pharmacy Introduction to Clinical Pharmacy, Concept of clinical pptx
Clinical Pharmacy  Introduction to Clinical Pharmacy, Concept of clinical pptxClinical Pharmacy  Introduction to Clinical Pharmacy, Concept of clinical pptx
Clinical Pharmacy Introduction to Clinical Pharmacy, Concept of clinical pptxraviapr7
 
How to Add a many2many Relational Field in Odoo 17
How to Add a many2many Relational Field in Odoo 17How to Add a many2many Relational Field in Odoo 17
How to Add a many2many Relational Field in Odoo 17Celine George
 
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRADUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRATanmoy Mishra
 
Prescribed medication order and communication skills.pptx
Prescribed medication order and communication skills.pptxPrescribed medication order and communication skills.pptx
Prescribed medication order and communication skills.pptxraviapr7
 
Human-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming ClassesHuman-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming ClassesMohammad Hassany
 
CapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptxCapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptxCapitolTechU
 
What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?TechSoup
 
Practical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptxPractical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptxKatherine Villaluna
 
In - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptxIn - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptxAditiChauhan701637
 
HED Office Sohayok Exam Question Solution 2023.pdf
HED Office Sohayok Exam Question Solution 2023.pdfHED Office Sohayok Exam Question Solution 2023.pdf
HED Office Sohayok Exam Question Solution 2023.pdfMohonDas
 
Ultra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptxUltra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptxDr. Asif Anas
 
3.21.24 The Origins of Black Power.pptx
3.21.24  The Origins of Black Power.pptx3.21.24  The Origins of Black Power.pptx
3.21.24 The Origins of Black Power.pptxmary850239
 
How to Show Error_Warning Messages in Odoo 17
How to Show Error_Warning Messages in Odoo 17How to Show Error_Warning Messages in Odoo 17
How to Show Error_Warning Messages in Odoo 17Celine George
 
CAULIFLOWER BREEDING 1 Parmar pptx
CAULIFLOWER BREEDING 1 Parmar pptxCAULIFLOWER BREEDING 1 Parmar pptx
CAULIFLOWER BREEDING 1 Parmar pptxSaurabhParmar42
 
AUDIENCE THEORY -- FANDOM -- JENKINS.pptx
AUDIENCE THEORY -- FANDOM -- JENKINS.pptxAUDIENCE THEORY -- FANDOM -- JENKINS.pptx
AUDIENCE THEORY -- FANDOM -- JENKINS.pptxiammrhaywood
 

Recently uploaded (20)

Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.
 
Prelims of Kant get Marx 2.0: a general politics quiz
Prelims of Kant get Marx 2.0: a general politics quizPrelims of Kant get Marx 2.0: a general politics quiz
Prelims of Kant get Marx 2.0: a general politics quiz
 
Quality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICEQuality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICE
 
How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17
 
Clinical Pharmacy Introduction to Clinical Pharmacy, Concept of clinical pptx
Clinical Pharmacy  Introduction to Clinical Pharmacy, Concept of clinical pptxClinical Pharmacy  Introduction to Clinical Pharmacy, Concept of clinical pptx
Clinical Pharmacy Introduction to Clinical Pharmacy, Concept of clinical pptx
 
Personal Resilience in Project Management 2 - TV Edit 1a.pdf
Personal Resilience in Project Management 2 - TV Edit 1a.pdfPersonal Resilience in Project Management 2 - TV Edit 1a.pdf
Personal Resilience in Project Management 2 - TV Edit 1a.pdf
 
How to Add a many2many Relational Field in Odoo 17
How to Add a many2many Relational Field in Odoo 17How to Add a many2many Relational Field in Odoo 17
How to Add a many2many Relational Field in Odoo 17
 
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRADUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
 
Prescribed medication order and communication skills.pptx
Prescribed medication order and communication skills.pptxPrescribed medication order and communication skills.pptx
Prescribed medication order and communication skills.pptx
 
Human-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming ClassesHuman-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming Classes
 
CapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptxCapTechU Doctoral Presentation -March 2024 slides.pptx
CapTechU Doctoral Presentation -March 2024 slides.pptx
 
What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?
 
Practical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptxPractical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptx
 
In - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptxIn - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptx
 
HED Office Sohayok Exam Question Solution 2023.pdf
HED Office Sohayok Exam Question Solution 2023.pdfHED Office Sohayok Exam Question Solution 2023.pdf
HED Office Sohayok Exam Question Solution 2023.pdf
 
Ultra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptxUltra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptx
 
3.21.24 The Origins of Black Power.pptx
3.21.24  The Origins of Black Power.pptx3.21.24  The Origins of Black Power.pptx
3.21.24 The Origins of Black Power.pptx
 
How to Show Error_Warning Messages in Odoo 17
How to Show Error_Warning Messages in Odoo 17How to Show Error_Warning Messages in Odoo 17
How to Show Error_Warning Messages in Odoo 17
 
CAULIFLOWER BREEDING 1 Parmar pptx
CAULIFLOWER BREEDING 1 Parmar pptxCAULIFLOWER BREEDING 1 Parmar pptx
CAULIFLOWER BREEDING 1 Parmar pptx
 
AUDIENCE THEORY -- FANDOM -- JENKINS.pptx
AUDIENCE THEORY -- FANDOM -- JENKINS.pptxAUDIENCE THEORY -- FANDOM -- JENKINS.pptx
AUDIENCE THEORY -- FANDOM -- JENKINS.pptx
 

Depositacion electroforetica dentro de campos electricos modulados

  • 1. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H View PDF VersionView Previous ArticleView Next Article DOI: 10.1039/C2RA01342H (Review Article) RSC Adv. , 2012, 2, 7633-7646 Electrophoretic deposition under modulated electric fields: a review Malika Ammam * Faculty of Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, ON L1H 7K4, CANADA. E-mail: m78ammam@yahoo.fr; Malika.Ammam@uoit. ca; Fax: 905-721-3304; Tel: (905)721-8668, ext 3625 Received 21st December 2011 , Accepted 16th May 2012 First published on the web 21st May 2012 Classical electrophoretic deposition (EPD) relies on continuous direct current (CDC) to deposit charged particles on electrodes. In recent decades, modulated electric fields such as pulsed direct current (PDC) and alternating current (AC) have been investigated. This paper reviews EPD under these modulated electric fields and major applications of the deposited microstructures. The paper starts with a short overview of EPD principals such as the electrical double layer of the charged particle, electrophoretic mobility and main suspension parameters including zeta potential, particle size, conductivity, viscosity and stability of the suspension. The EPD mechanisms from the earliest model reported by Hamaker and Verwey to latest models including Sarkar and Nicholson model and influence of the electrohydrodynamics and electroosmosis as well as electrode surface and its electrochemical double layer on the deposition process have been briefly discussed. Two categories of modulated electric fields, PDC and AC fields http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (1 de 39) [31/01/2014 02:10:17 p.m.]
  • 2. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H have been addressed with their advantages and disadvantages. It is found that compared to CDC, PDC offers the advantage of: i) reducing the coalescence between gas bubbles induced by water electrolysis from aqueous suspensions, hence yielding deposition of smooth and uniform coatings, ii) reducing aggregation and disaggregation of nanometer sized particles, leading to formation of uniform and homogenous deposits and, iii) PDC generates low change in pH near the electrode, thus it is convenient for deposition of biochemical and biological species in their highly active states. The main disadvantage of PDC over CDC lies in the decrease of the deposition yield. The latter can be more pronounced if low time-pulses are used. Various categories of AC signals including symmetrical fields with no net DC component and asymmetrical AC signals without and with net DC component have been discussed. Overall, the deposition rate under AC fields increases with polarization time and amplitude. With respect to frequency, the deposition rate increases with frequency up to certain value then drops at elevated frequencies. It is noted that deposition under AC signals offers the possibility to produce superior quality coatings from aqueous suspensions because electrolysis of water as well as particle orientation during the deposition could be controlled. From the application standpoint, PDC and AC, offers new application perspectives such as in biotechnology. Because under modulated electric fields, EPD can now be accomplished from aqueous suspensions with low water electrolysis rates, a variety of biochemical and biological species can be deposited to yield highly active layers suitable for a wide range of applications including biosensors, biofuel cells and bioreactors. http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (2 de 39) [31/01/2014 02:10:17 p.m.]
  • 3. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H Malika Ammam Malika Ammam received her MS degree from the University of Pierre et Marie CURIE in July 2002 and her PhD from the University of Paris Sud XI, France in September 2005. From 2006 to 2007, she worked as a research fellow at the University of Kansas in collaboration with Pinnacle Technology Inc. (US). From 2007 to 2010, she worked as a research associate at KU Leuven, Belgium and she is currently working at the University of Ontario Institute of Technology in collaboration with Alcohol Countermeasure Systems Corporation, Canada. Electrophoretic deposition, electrochemistry, materials, sensing and energy are among her research projects and interests. 1. Introduction Electrophoretic deposition (EPD) is an important technology for colloidal coating processes. Fig. 1 illustrates a schematic representation of an EPD cell. Under the influence of direct current (DC) electric field, the charged colloids or particles suspended or dispersed in a fluid move towards the electrode and deposit.1–4 Depending on surface charge of the suspended particles, two kind of EPD can be defined. If the particles are positively charged (Fig. 1), they will move towards the electrode with the opposite sign, the cathode, and this process is called cathodic EPD. By contrast, if the dispersed particles are negatively charged, they will be attracted by the positively charged electrode, the anode, and this process is named anodic EPD. http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (3 de 39) [31/01/2014 02:10:17 p.m.]
  • 4. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H Fig. 1 Schematic diagram of electrophoretic deposition of charged particles on the anode of an EPD cell with planar electrodes. In EPD, upon application of a potential, a current will flow between the parallel plate electrodes (Fig. 1). The magnitude of the current that flows is influenced by a variety of system parameters, including the cell constant, the solution conductivity, and interfacial electrochemical kinetics. The electric field strength in the suspension (E) is related to the current density (J) and the conductivity of the suspension (k), which is nothing more than the microscopic formulation of the Ohm's law (J = kE). Basic EPD is accomplished from organic suspensions that have several advantages including low conductivity and good chemical stability of the suspension and absence of the electrochemical reactions and Joule heating at the electrodes. This leads to formation of high quality coatings. Nevertheless, the use of organic solvents is associated with many problems including the cost, volatile, toxicity most of the time and flammability. Furthermore, because organic solvents have low dielectric constant (dissociation power), this induces a limited particle charge. Thus, high electric fields strengths are required to move the suspended particles towards the electrode. EPD from aqueous suspensions is a good alternative for solving many problems associated with the organic solvents such as the cost and the environmental load. Furthermore, because the dissociation power of water is high (dielectric constant 80.1), this results in a buildup of a charge of the particle. Consequently, low electric fields strengths can be used. The main http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (4 de 39) [31/01/2014 02:10:17 p.m.]
  • 5. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H disadvantage of EPD from aqueous suspensions is water electrolysis. Above the thermodynamic voltages of water oxidation and reduction,5 electrochemical reactions occur at the electrodes and generate gases, O2 at the anode and H2 at the cathode (details on the reactions can be found in section 3.1.1.). The formed gas bubbles can be incorporated in the deposit and yields damaged and poor quality coatings. To overcome this problem, several approaches have been made. The first attempted approach was to carry out the EPD process at voltages below the thermodynamic values of water electrolysis. This provided successful production of alumina microstructures.6 However, the low applied voltages yielded only low deposition rates that are limited to small wall thicknesses. Other concepts based on sacrificial electrodes and competitive reactions have been explored. For example, Chronberg and Händle7 employed zinc (Zn) rollers as deposition electrodes to compete the oxidation reaction of water with that of Zn, a more facile reaction. Nonetheless, low deposition rates as well as contamination of the coatings with Zn limited the process. Materials that store gases such as palladium (Pd) have also been investigated as cathodes for H2 storage.8 Unfortunately, only small amount of H2 can be stored within the material. Finally, chemical additives such as hydroquinone were found to be useful for suppressing O2 evolved at the anode.9,10 But, the concept is only helpful under particular conditions such as alkaline pH. One promising method to deal with electrolysis of water during the EPD process from aqueous suspensions is by using membranes.11–15 A porous and ion-permeable membrane is placed between the anode and the cathode, hence dividing the EPD cell into two chambers. The deposition occurs on the membrane itself, but the ions can pass through the membrane pores to recombine at the electrodes and form gases. The sufficient distance which separates the membrane from the electrodes allows formation of free-bubble deposits. The membrane based process was successfully used to deposit different materials such as alumina, silica glass and zirconia. Another efficient means to decrease the amount of the evolved gas bubbles at the electrodes and allow formation of homogenous deposits from aqueous suspensions is to carry out the EPD process under modulated electric fields such as pulsed direct current (PDC) and alternating current (AC). Some examples of these signals are shown in Fig. 2. The basic difference between continuous direct current (CDC) shown in Fig. 2A and PDC of Fig. 2B is that the voltage of a CDC is roughly constant, whereas the voltage of a PDC wave continually varies, but like a DC wave, the sign of the voltage is constant. In AC, the voltage continually varies between positive and negative values. It is worth noting that the rectangular waveform of Fig. 2 constitutes only http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (5 de 39) [31/01/2014 02:10:17 p.m.]
  • 6. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H one example of a theoretical infinite number of waveforms. In AC, if voltage-time of the positive and negative half cycles is equal, the waveform is symmetrical with theoretically no net DC component (Fig. 2C). However, if voltage-time of the two half cycles is different, the AC wave is asymmetrical and, depending on whether the surface areas of both half-cycles are equal or not, the wave can be asymmetrical with net DC component (Fig. 2D) or, asymmetrical with no net DC component (Fig. 2E). Fig. 2 Schematic representation of some electrical signals: (A) continuous direct current (CDC), (B) pulsed direct current (PDC), (C) symmetrical alternating current (AC) with no net DC component, (D) asymmetrical AC signal with net DC component and, (E) asymmetrical AC wave with no net DC component. In recent decades, these modulated electric fields have been investigated not only for EPD of ceramic and polymer particles but also for biochemical and biological species that are more sensitive to pH shifts or electrochemical reactions products formed at the electrodes. Because http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (6 de 39) [31/01/2014 02:10:17 p.m.]
  • 7. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H modulated electric fields generate a low rate of water electrolysis, biochemical and biological species can be deposited in their highly active states. For instance, EPD of bacterial cells and enzymes from aqueous solutions under CDC has been reported to some extent.16 However, it is not clear from the text whether the activity of the species after CDC that generates a high amount of electrolysis was examined or not. This paper reviews some selected literature dealing with EPD under modulated electric fields, PDC and AC, and the main applications of the deposited microstructures. However, first some necessary reminders and updates about EPD principles should be addressed. 2. EPD principals 2.1. Electrical double layer and electrophoretic mobility Charged particles in a fluid are surrounded by a cloud of ions. Ions of opposite charge (counterions) are attracted towards the surface of the charged particle, while ions of similar charge are pushed away from that surface. This yields a net electrical charge on one side of the interface and a charge of opposite sign on the other side of the interface, giving rise to what is called the electrical double layer of the particle. The widely accepted model for the particle double layer is the Stern model.17 A schematic representation of the particle electrical double layer with distribution of charged species and potential drop across the double layer in accordance with Stern model is shown in Fig. 3. If we assume a negatively charged particle, the ions of opposite charge closest to surface of the particle form what is known as a Stern layer and the rest of the ions which are distributed more broadly, form what is called the diffuse double layer (Fig. 3). The particle surface at the plane of shear between Stern and the diffuse layer is characterized by a potential called zeta potential, ζ, which is involved in nearly all electrokinetics.18,19 Application of an external electric field can shear away some of the ions outside the Stern layer and yields a drift and migration of the particle towards the electrode of opposite charge (Fig. 1). http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (7 de 39) [31/01/2014 02:10:17 p.m.]
  • 8. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H Fig. 3 Schematic representation of the electric double layer of the charged particle and potential drop across the double layer. (a) Surface charge, (b) stern layer, (c) diffuse layers of counter-ions. Image reproduced from ref. 1 with permission of Elsevier. The main electrophoretic characteristic of the particle under the influence of the electric field is called electrophoretic mobility, μeph, which can be defined as the coefficient of proportionality between the electric field strength, E, and the particle velocity, Veph:19–21 Veph = μephE (1) In turn, the electrophoretic mobility increases with the particle zeta potential, ζ, and decreases with the viscosity of the media, η The coefficient of correlation between μ and ζ depends on the size of the particles. The electrophoretic mobility of small particles defined as having a radius r much smaller than the Debye length of the counterionic atmosphere (r ≪ 1/k) is described by the Huckel equation: μeph = 2εε0ζ/3η (2) where ε and ε0, are the dielectric permittivity of the media and vacuum, respectively. The electrophoretic mobility of particles of size much greater than the Debye length of the counterionic layer (r ≫ 1/k) is given by the Helmholtz–Smoluchowski equation: http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (8 de 39) [31/01/2014 02:10:17 p.m.]
  • 9. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H μeph = εε0ζ/η (3) The displacement of a particle for a finite time Δt under uniform DC electrophoresis can reasonably be defined as21 : xDC = μephEDCΔt + x0 (4) where the constant x0 determines the initial location of the particle. 2.2. Key suspension parameters EPD is a two-step mechanism. First, the particles must migrate to the deposition electrode under the action of an electric field and, second, the particles must coagulate and deposit on the electrode (Fig. 1). There are a number of suspension parameters that influence the EPD process as well as the quality of the deposited coating. Some of the important ones are discussed below. 2.2.1. Zeta potential. Zeta potential is a key parameter. The dispersed particles are required to have an elevated and a uniform surface charge, which will determine their stability in the suspension. The stability of the charged particles is essentially governed by the sum of the attractive and the repulsive forces between the particles, mainly electrostatic and van der Waals in nature. To prevent agglomeration between particles, high particle charge is required to create high electrostatic repulsion. By contrast, if the particle charge is low, the particles will coagulate. The particle charge or zeta potential can be controlled by various charging agents such as acids, bases, or specifically adsorbed polyelectrolytes.22 However, before using charging agents to increase the charge of the suspended particles, the first common step in suspension preparation is powder washing. This step allows the removal of any residual impurities that are incorporated with the powder and may affect the stability of the suspension, thus the deposition characteristics. Basu et al.23 reported that unwashed powder led to an unstable suspension, which in turn led to lower deposition yields and a decrease in green density of the deposit by about 15–25%. The problem was solved by repetitive washing of the powder with deionized water. Also, during the washing process, significant reduction in the conductivity of the supernatant was observed.23 Hence, it can be concluded that the washing process is an important factor in suspension stability. While the washing process can easily be accomplished with inorganic materials such as ceramic http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (9 de 39) [31/01/2014 02:10:17 p.m.]
  • 10. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H particles,23 for biomolecules and biological cells, this step might be difficult. Because enzymes and biological cells usually contain salts for electroneutrality, their dispersion, even in ultrapure water gives rise to high conductivity suspensions, which in turn may affect their zeta potential as well as the suspension stability.24–26 The charge on a biomolecule such as enzymes, proteins or biological cells arises from the ionization of the functional groups present within the biomolecule. In proteins or enzymes, these groups carried out by essentially the amino acids residues give rise to either positive or negative charges. In acidic pH, the net charge of the enzymes is usually positive, whereas in alkaline pH, the charge is negative. At a certain pH, enzymes will have no net charge, called isoionic point, which is around pH 4 for glucose oxidase for example. At neutral pH, enzymes such as glucose oxidase are negatively charged and the zeta potential of enzymes depends largely on the dissolving media. Matsumoto et al.27 measured the zeta potential of glucose oxidase dissolved in high ionic strength phosphate buffer solution as −0.4 mV. This led to practically no electrophoretic mobility of the enzyme. This problem can be solved if the enzyme is dissolved in ultrapure water. Ammam and Fransaer24 measured the zeta potential of glucose oxidase dissolved in ultrapure water containing low amount of NaOH as charging agent as −10.7 mV. The latter led to a net electrophoretic mobility of the enzyme when asymmetrical AC fields are applied to form thick deposits on the electrode. For biological cells, the washing procedure is easier than for enzymes and proteins because cells can be dispensed in water and filtered off to remove the excess salts. Consequently, adequate zeta potentials of cells suspended in water have been recorded.16,28,29 A typical example on how zeta potential varies with pH of the suspension is shown in Fig. 4 for E. Coli microorganism and inclusion bodies.16 The isoionic point of these species is located at pH 3–4. At higher pH, the species are negatively charged, whereas at lower pH, the species are positively charged. The charge or zeta potential of the species increases when pH is moved away from the isoionic point. Dependence of zeta potential on pH for a suspension of pure E. Coli bacteria and a suspension of pure inclusion bodies. Image reproduced from ref. 16 with permission of Elsevier. http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (10 de 39) [31/01/2014 02:10:17 p.m.]
  • 11. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H Fig. 4 Dependence of zeta potential on pH for a suspension of pure E. Coli bacteria and a suspension of pure inclusion bodies. Image reproduced from ref. 16 with permission of Elsevier. 2.2.2. Particle size. Particle size is an important parameter in the EPD process. For stable suspension, it is important that the dispersed particles remain well dispersed and stable to yield homogenous and uniform deposits. For ceramic particles, it is reported that the optimal range of particle size lies between 1–20 μm.30 The problem with larger sizes is that the particles tend to sediment under the gravitational forces leading in vertical cells to thick deposits on the bottom and thin films on top. Likewise, very small particles tend to aggregate and thus yield inhomogeneous deposits. 2.2.3. Conductivity and viscosity of the suspension. In EPD, the amount of the deposited particles is related to the strength of the electric field. The applied electric field between the anode and cathode is not only carried by the charged particles but mostly by the free coexisting ions (electrolyte). On the other hand, the amount of the coexisting ions determines the conductivity of the suspension, an important factor in EPD. If the conductivity of the suspension is too high, i.e., the amount of the free ions is considerable, the particle mobility decreases because the zeta potential is reduced.26 By contrast, if the conductivity is too low, the suspension will be resistive, leading to loss in stability.25 In turn, the conductivity is related to dielectric constant or dissociation power of the solvent. It is reported that optimal deposition rates are obtained with liquids having dielectric constant in the range of 12–25,31 specifically associated with organic solvents. With liquids having high dissociation power such as water (dielectric constant 80.1 at 20 °C), the amount of ions in the suspension must be very low in order to yield stable suspension, hence high deposition rate. Also, viscosity accounts in EPD process. The amount of the dispersed particles and the pH affect the viscosity of the suspension.25,32 Low viscosities are required for successful EPD and optimal dispersant concentration can experimentally be determined.32 2.2.4. Suspension stability. A stable suspension with well-dispersed and controlled surface charge is essential for successful EPD.25 The stability of the suspension is characterized by the http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (11 de 39) [31/01/2014 02:10:17 p.m.]
  • 12. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H rate and tendency of the charged particles to undergo or avoid flocculation. The suspension stability depends on several factors such as size of the particles, their zeta potential, Debye length of the solution as well as the presence of adsorbed species. Average sized particles with uniform surface charge tend to stay suspended for long periods due to Brownian motions. Bigger sized particles tend to sediment because of the strong gravitational forces, thus require continuous hydrodynamic agitation to stay in the suspension. Stable suspension shows no flocculation or sedimentation of the particles. However, if the suspension is too stable, meaning that the repulsive forces between the particles are too strong, the electric field will not be able to overcome these forces and move the particles towards the electrode, thus there will be no deposition. Near the electrode, if the suspension remains stable, there will be no deposition. Fortunately, presence of other phenomena such as electrochemical reactions, electroosmosis and electrohydrodynamic flows induce instability near the electrode and cause the particles to fluctuate and precipitate. 2.3. EPD mechanisms After migration of the charged particles from the bulk to the electrode of opposite charge, the next step in EPD process is the coagulation and deposition. Although EPD is known since the 19th century, the deposition mechanisms are not fully understood and still under debate. Several theories have been proposed. The earliest dates back to 1940s. Hamaker and Verwey33 suggested that deposition is due to accumulation of the charged particles on the electrode under the action of the applied electric field. Nevertheless, the proposed mechanism is more useful for deposition of particles on a membrane placed between two electrodes, rather than for deposition on the electrode. In 1992, Grillon et al.34 suggested that EPD occurs by particle charge neutralization. The charged particle approaching the electrode neutralizes upon contact with the opposite charge of the electrode and precipitate. The drawback of this theory is that the deposition is limited to a monolayer and this cannot explain the formation of thick coatings. Few years later, Koelmans35 and later De and Nicholson36 proposed that deposition is governed by electrochemical particle coagulation. Due to electrochemical reactions at the electrodes during the EPD process, the ionic strength near the electrode surface would increase compared to bulk. This induces a reduction of the repulsive forces between particles near the electrode, which in turn lowers zeta potential and induces precipitation. This theory is useful to explain deposition of particles from suspensions containing water but not EPD from organic suspensions since no electrochemical reactions occur. http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (12 de 39) [31/01/2014 02:10:17 p.m.]
  • 13. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H To overcome the problem dealing with coagulation in absence of the electrochemical reactions, Sarkar and Nicholson17 suggested that deposition occurs through the double layer distortion and thinning, followed by coagulation of the particles on the electrode. As illustrated in Fig. 5, three main successive steps take place: i) When the charged particle that is surrounded by the diffuse double layer is subjected to an electric field, it undergoes a distortion and becomes thinner ahead and wider behind. ii) During the migration of the charged particle, ions of similar charge will move in same direction of the particle and can react with the counter ions accompanying the charged particle. The latter induces a thinning of the double layer of the particle. iii) Because the double layer of the particle is now thinner, it can easily approach another particle with also a thinner double layer and, if the contact is close enough to favor van der Waals attractive forces, the deposition occurs. So far, no experimental data have yet been presented to support this theory. However, thanks to imagery techniques, experimental data are now available on how the particles aggregate on the electrode. The aggregation is modeled by various mechanisms such as electrohydrodynamics37 and electroosmosis.38,39 The action of an electric field on charge of the particle diffuse layer gives rise to the electroosmotic flow, while action of an electric field on charge induced by the electric field on the electrode gives rise to the electrohydrodynamic flow. For electroosmosis, thickness of the electrical double layer of the particle, particularly, the diffuse layer is a key determinant of the electroosmotic forces. A thick diffuse layer yields significant electroosmotic forces, while a thin diffuse layer gives rise to negligible electroosmotic forces.39 http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (13 de 39) [31/01/2014 02:10:17 p.m.]
  • 14. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H Fig. 5 Electrical double layer distortion and thinning mechanism for electrophoretic deposition. Image reproduced from ref. 17 with permission of Wiley & Sons. Also, the electrode surface and its electrochemical double layer play an important role in the deposition process.5,40 Polarizable electrodes create a substantial potential drop in the electrochemical double layer of the electrode, thus most of the current is capacitive. Consequently, the electric field strength reduces in the bulk of the suspension and induces instability. By contrast, non-polarisable electrodes generate minimum drop current and most of the current is Faradaic. This induces an effective electric strength in the bulk of the suspension. Prieve et al.40 have recently reviewed 2D assembly of particles under DC and AC electric fields http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (14 de 39) [31/01/2014 02:10:17 p.m.]
  • 15. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H and emphasized the role of the electrochemical double layer of the electrode in the deposition process. 3. EPD under modulated electric fields 3.1. PDC fields The advantages of PDC shown in Fig. 2B over CDC of Fig. 2A for EPD of charged particles can be summarized as: i) PDC significantly reduces the coalescence between gas bubbles induced by water electrolysis. Thus, yields deposition of smooth and uniform coatings. ii) PDC reduces aggregation between nanometer sized particles, leading to formation of uniform and homogenous deposits. iii) PDC generates low change in pH near the electrode. Hence, is convenient for deposition of biochemical and biological species in their highly active states. 3.1.1. Reduction in coalescence between gas bubbles. PDC has been investigated for EPD of ceramic particles,41–46 polymers,47 carbon nanotubes48 and enzymes.49 In all cases, low rates of gas bubbles have been noticed when PDC is used. Fig. 6 depicts typical topographies of alumina deposits produced from aqueous suspensions using CDC and PDC with various time-pulses. It can be seen that under CDC, the deposits are porous and inhomogeneous. This is due to water electrolysis, which forms gases, O2 at the anode and H2 at the cathode, following the reactions I to IV:5 http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (15 de 39) [31/01/2014 02:10:17 p.m.]
  • 16. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H Fig. 6 Surface morphology of deposits obtained by PDC EPD at constant voltage mode of 20 V (A) and at constant current mode of 0.004 A (B). Image reproduced from ref. 46 with permission of Elsevier. Anode: 2H2O = O2 + 4H+ + 4e− (Eo = −1.23 V vs. NHE) (I) 4OH− = O2 + 2H2O + 4e− (Eo = −0.40 V vs. NHE) (II) Cathode: 2H+ + 2e− = H2 (Eo = 0 V vs. NHE) (III) 2H2O + 2e− = H2 + 2OH− (Eo = −0.83 V vs. NHE) (IV) The dominant reaction would of course depend on whether the aqueous suspension contains sufficient amounts of H+, OH− or only water. For example, if the solution contains a sufficient amount of OH−, OH− would be the first species to be oxidized into O2 at the anode because the reaction requires less voltage (−0.4 V) than that of water oxidation (−1.23 V). Similarly, if H+ were added to the aqueous suspension, H+ would be the first species to be reduced into H2 at the cathode because the reaction requires 0 V compared to reduction of water molecules (−0.83 V). However, if pure water is used as a fluid suspension, after the reduction and oxidation of the small amount of H+ and OH− present at the concentration of 10−7 M, water molecule will be the main species to be oxidized at the anode and reduced at the cathode with voltages of −1.23 V and −0.83 V, respectively. During EPD process, the generated gas bubbles can be incorporated in the deposit, and results in http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (16 de 39) [31/01/2014 02:10:17 p.m.]
  • 17. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H porous morphologies (CDC of Fig. 6). By comparison, under PDC, the number and size of the pores can be reduced if time-pulses are decreased. Theoretically, once the thermodynamic voltages of water electrolysis are reached, water starts to decompose into O2 and H2. Nevertheless, depending on the reaction conditions such as nature of the electrode material, nature of the electrolyte and its concentration etc., the potentials may shift from the thermodynamic values. The latter defines the kinetics of water electrolysis reactions. Besra et al.46 measured larger shifts in pH near the electrode using CDC compared to PDC. This may suggest that PDC induces low rates of electrolysis compared to CDC. However, taking into account the total polarization time (ON + OFF) used for PDC that is higher than that used for CDC since CDC has no OFF-time, it is possible to propose that using PDC, the reaction products formed during the ON-time diffuse towards the bulk solution during the OFF-time, inducing less change in pH near the electrode. Thus, it maybe concluded that unless extremely low time-pulses are used,50 PDC probably do not generate low rates of electrolysis, but more appropriately it minimizes coalescence between gas bubbles, thus preventing formation of larger ones. Fig. 7 supports this claim. It shows a comparison between SEM images of polypyrrole (PPy) coatings on glassy carbon (GC) substrates produced by electropolymerization of pyrrole monomer from low conductivity solutions using CDC (Fig. 7A, 7B and 7C) and PDC (Fig. 7D).51 The same deposition time is used for all coatings. In addition, 10 s is used as time-pulse for PDC that is large enough to induce formation of gas bubbles since micro-meter sized bubbles were observed even with pulses of 0.1 ms.50 Fig. 7A, 7B and 7C clearly depict rough and inhomogeneous topographies of PPy deposits under CDC. This is due to the large amount of gas bubbles incorporated in the coatings. More importantly, Fig. 7C clearly shows that under CDC, the gas bubbles coalesce and when maximum volumes are reached, the bubbles explode and form patterns that can be described as “open flowers”. By comparison, the topography of PPy coating obtained by means of PDC is smoother and homogenous (Fig. 7D). Interruption of the field during OFF-time for PDC breaks apart most of the tiny formed bubbles. Hence, prevent their coalescence during the next ON-time polarization. http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (17 de 39) [31/01/2014 02:10:17 p.m.]
  • 18. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H Fig. 7 SEM images of electrodeposited polypyrrole (PPy) from pyrrole aqueous solutions using CDC (A, B, C) and PDC (D) at 4 V vs. Ag/AgCl for equal ON-time deposition mode. Part of the image reproduced from ref. 51 with permission of Elsevier. 3.1.2. Reduction of aggregations between particles. The second advantage of PDC over CDC is that PDC prevents the particles near the electrode from aggregation. Fig. 8A and 8B depict SEM images of 2D polystyrene particles deposited by means of PDC and CDC, respectively.47 While aggregation between particles can be observed with CDC (Fig. 8B), the monolayer formed by means of PDC depicts more independent particles (Fig. 8A). Under PDC, the decrease in aggregation between the particles can be assigned to: i) Reduction in the electroosmotic flow that is induced near the electrode (Fig. 8C). In other words, when an electric field is applied between the anode and the cathode, the charged particles move towards the electrode of opposite charge. As the particles approach the electrode, the electroosmotic forces induced by the electric field interfere within the Debye length range and bend the electrophoretic forces. This causes their aggregation in CDC. Under PDC, the electroosmotic flow stops during the OFF-time and when the next ON-time starts, the particles near the electrode move under electrophoresis, without significant interference from electroosmosis and thus deposit independently.47 http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (18 de 39) [31/01/2014 02:10:17 p.m.]
  • 19. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H ii) Reduction in coalescence between the formed gas bubbles. In other words, under CDC, electrolysis of water induces large-sized bubbles that may generate a pressure on the surrounding particles and push them away. As a result, the particles will be gathered in between the formed gas bubbles and aggregate as in Fig. 8B. By comparison, because PDC prevent gas bubbles from coalescence and reduce their size, the pressure applied by the formed bubbles should also be reduced. This yields deposition of independent particles at 2D (Fig. 8A) and 3D.43 Single-size deposit particles by PDC (A) and CDC polarisation (B). All particles are deposited at 3.3 V cm−1 for 2 min. (C) Illustration of on-going deposit particles during EPD. The effect of electrokinetic phenomena is to induce the on-going particles as they approach the substrate. The off-mode condition reduces the effect of electroosmosis on an incoming deposit particle (particle 2). Image reproduced from ref. 47 with permission of Elsevier. Fig. 8 Single-size deposit particles by PDC (A) and CDC polarisation (B). All particles are deposited at 3.3 V cm−1 for 2 min. (C) Illustration of on-going deposit particles during EPD. The effect of electrokinetic phenomena is to induce the on-going particles as they approach the substrate. The off-mode condition reduces the effect of electroosmosis on an incoming deposit particle (particle 2). Image reproduced from ref. 47 with permission of Elsevier. 3.1.3. Preservation of the activity of deposited biomolecules. PDC is advantageous over CDC http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (19 de 39) [31/01/2014 02:10:17 p.m.]
  • 20. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H for EPD of biomolecules such as enzymes.49 Because PDC yields low change in pH near the electrode,46 consequently, the activity of the deposited enzyme is preserved. Ammam and Fransaer49 noticed a decrease in activity of the deposited enzyme by 25% when they switched from PDC to CDC under the same conditions. 3.1.4. Disadvantages of PDC over CDC. The main disadvantage of PDC over CDC is the decrease in the deposition yield. The latter can be more pronounced if low time-pulses are used as depicted in Fig. 6.42,46 Although the deposition mechanisms under PDC still under investigation, if sufficient time-pulses are employed, accumulation of the particles on the electrode is attributed to the strong inertia forces induced by the PDC field. This results in migration of the particles near the electrode for a few more seconds following the OFF-time mode to reach the electrode and deposit without bubbles.46 The reduction in the deposition yield using PDC is attributed to the low change in pH near the electrode, which slow down the charged particles located near the electrode to reach their isoelectric point and precipitate.35,36,46 3.2. AC fields While in DC fields the electric charge flows only in one direction, in AC fields the movement of the electric charge periodically reverses direction between the positive and negative (Fig. 2). As a consequence, under an AC field the dynamic of particles are much more complicated than in DC. Thus, analysis of the experimental observations is often difficult because there are a number of phenomena and forces that arise from the interaction of the AC field with the suspended particle, and this is influenced by a range of parameters including frequency, particle size, electrolyte conductivity, electric field distribution, and whether the current passes through the capacitance of the electrode double layer or, through the electrochemical reaction.40,52–60 Some of the forces are well-studied and documented in literature such as electrophoresis,61–63 dielectrophoresis,64–67 electrorotation68,69 and travelling-wave dielectrophoresis.70 The basic difference between these forces is schematically depicted in Fig. 9. http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (20 de 39) [31/01/2014 02:10:17 p.m.]
  • 21. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H Fig. 9 Schematic representation of a charged particle under the influence of electrophoresis (A), dielectrophoresis (B), electrorotation (C) and travelling wave dielectrophoresis (D). Electrophoresis. In electrophoresis (Fig. 9A), a dispersed charged particle in a fluid moves and migrates under the action of a uniform electric field towards the electrode of opposite charge. Dielectrophoresis. If the electric field is not uniform as illustrated in Fig. 9B, the interaction between the induced dipole and the non-uniform electric field generates a force. Due to presence of the electric field gradient, these forces are not equal in magnitude and generate net movement of the charged particle under dielectrophoresis. Electrorotation. If the electric field is rotating as depicted in Fig. 9C, a dipole is induced across the particle, which will simultaneously rotate with the electric field. If the angular velocity of the rotating field is large enough, this will require certain time to form a dipole on the particle, which will lag behind the field. The non-zero angle between the field and the dipole induces the particle to rotate in the field and gives rise to electrorotation. Travelling wave dielectrophoresis. Travelling wave dielectrophoresis is a linear form of http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (21 de 39) [31/01/2014 02:10:17 p.m.]
  • 22. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H electrorotation. As displayed in Fig. 9D, instead of a circular arrangement, the electrodes are arranged in a linear manner with 90° phase shift from each other. An electric field wave is produced between the electrodes and interaction between this wave and the polarizable particle induces a dipole that will move with the electric field. If the field wave is strong enough, the dipole will lag behind the field just like in electrorotation. However, because the electric wave is travelling in linear instead of circular manner, a force, rather than a torque will be induced, thus leading to a drift of the particle from one electrode to another. Therefore, as one can imagine, under AC fields, various phenomena could occur simultaneously and the deposition mechanisms are often unclear. For example, at low frequencies, the interaction between the charged particle and the field gives rise to electrophoresis. AC field also produces a frequency dependent dipole on a polarisable suspended particle and depending on the field distribution; interaction between the dipole and the electric field can generate dielectrophoresis, electrorotation and travelling wave dielectrophoresis (Fig. 9). Furthermore, if the AC field is strong enough, it induces a fluid flow and heating at the electrodes. The AC field can interact with the fluid to produce electrohydrodynamic and electroosmotic forces as well as electrothermal due to Joule heating. The resulting fluid flow may induce a drag force on the particle and thus a motion. Depending on the frequency and the ionic conductivity (electrolyte), the electrohydrodynamic flow may induce aggregation or separation between the suspended particles near the electrode. At high frequencies, electrothermal fluid flow competes with the dielectrophoretic forces and electrohydrodynamics account. At low frequencies, AC electroosmotic flow dominates and this is strong even at low potentials. At intermediate frequencies, both electrohydrodymics and electrosmosis are active. On top of all the applied forces, particle–particle interaction and Brownian motion occur continuously. Because of the complicated dynamics of particles under AC fields, the formulas describing the displacement of the charged particles in the AC field are also complicated if compared to the simple DC formula shown in equation (4). The displacement of charged particles in AC fields will depend essentially on nature of the AC waveforms (sine, triangular, rectangular etc.) as well as the symmetry or asymmetry of the signal, which will define the mathematical formulas.20,21 For example, in case of an harmonically oscillating electric field, the amplitude of the peak-to- peak displacement, xAC, of the charged particle is reported as:21 xAC = −[μeph/EAC/sin(ωt)]/ω + x1 (5) http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (22 de 39) [31/01/2014 02:10:17 p.m.]
  • 23. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H where EAC is the peak to peak amplitude, ω is the applied angular frequency, μeph is the electrophoretic mobility and x1 determines the center of the trajectory. 3.2.1. Symmetrical AC fields with no net DC component. Symmetrical AC-electric fields have been used since the 19th century for EPD of charged particles. This can be found in a large number of patents typically for industrial applications such as electro-coating of paint based polymers and copolymers.71 A typical example of symmetrical AC waveform that generates no net DC component is shown in Fig. 2C. What theoretically can be predicted using symmetrical and uniform AC waveforms is that at low frequencies and during the first half-cycle of the period, the charged particle moves a certain distance, d. During the other half-cycle, the particle changes its direction back to its original position, −d. Consequently, the particle oscillates around a fixed spot in the fluid between the two electrodes and its net migration becomes zero.20,72 Therefore, it can be concluded that symmetrical and uniform AC signals would not be appropriate for an efficient EPD. Nevertheless, a large number of scientists have succeeded to deposit thin and even thick coatings using symmetrical waves. In view of this, in 1979, Ul'berg et al.73 deposited weakly charged submicron oligomeric epoxy resin particles. Later, Hirata et al.74 reported EPD of alumina particles under symmetrical sine waves from aqueous suspensions at voltage of 6 V and frequencies of 0.12, 1, and 10 kHz. In the past decade, Poortinga et al.75 investigated symmetrical AC signals for EPD of spherical and rod-shaped bacterial cells and noticed that the bacterial cells adhere and deposit on the electrode if sufficiently high currents are used. Although the deposition mechanisms under these signals are not fully understood, the formed monolayers have been attributed by Ul'berg et al.73 and Hirata et al.74 to diffusion (inertia free) since the particles were observed to coagulate on the electrode instantly. On the other hand, other phenomena such as electrohydrodynamic and electroosmotic forces may account in the deposition process. In this context, Sides54 reported that when the frequency changes, the interaction strength between the particles near the electrode can reach its maximum and it can even reverse attractive to repulsive forces and vice versa leading to aggregation of the particles on the electrode.54 So far, when uniform and symmetrical AC signals are used, low deposition rates that are limited to monolayers were usually depicted.28,74,75 There are some reported contradictory observations, where, using symmetrical or uniform AC signals, thick deposits were obtained. For example, Gardeshzadeh et al.76 deposited thick films of multiple walled carbon nanotubes using square and http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (23 de 39) [31/01/2014 02:10:17 p.m.]
  • 24. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H sine waves at frequencies of 1–1000 Hz as well as thick films of SnO2.77 Heidari et al.78,79 followed the procedure by Gardeshzadeh and obtained thick films. Also, Riahifar et al.72,80 employed similar category of electrodes as Heidari and deposited thick TiO2 films. According to theoretical predictions, these symmetrical signals should not form thick deposits. The latter might be related to the setup used to carry out the deposition. Non-planar and non- parallel electrodes have been employed. An example of the electrodes configuration is illustrated in Fig. 10. This configuration suggest generation of non-uniform electric fields which will give rise to not only electrophoresis, but to eventually other forces such as dielectrophoresis and travelling wave dielectrophoresis of the particles from one electrode to another. Fig. 10 Optical microscopy image of the electrode configuration used by Heidari et al.79 to deposit WO3 particles. Because space between the electrodes is only hundreds of μm, the particles have connected the electrodes together. Image reproduced from ref. 79 with permission of Springer. The main characteristics of EPD under symmetrical AC waveforms is that the deposition rate increases by reducing the frequency72,73,75 and increasing the voltage.72,73 Also, the deposition http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (24 de 39) [31/01/2014 02:10:17 p.m.]
  • 25. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H yield augments with the polarization time then reaches a saturation plateau.73,77 3.2.2. Asymmetrical AC field with net DC component. A typical example of asymmetrical AC wave with net DC component is shown is Fig. 3D. Because the surface area voltage–time (E–t) of the positive and negative half-cycles are not equal, a DC component is induced. This leads to a net drift of the charged particle towards the electrode of opposite charge. Furthermore, under this category of signals, inertia forces could also be an important driving force for migration of the particles because, during the fast voltage change from the positive to the negative signal and vice versa, the particles are accelerated and they cannot slow down open the reverse signal. The latter has been experimentally observed by Nold and Clasen,81 who recorded at the output a supplementary peak every third peak that has initially not been programmed. The advantage of the asymmetrical AC signal with net DC over pure DC consists of producing superior quality coatings because electrolysis as well as particle orientation during deposition could be controlled to some extent. In view of this, Shindo et al.82 employed AC signals with controlled reverse current to < 10% to form coatings with superior corrosion resistance. Nold and Clasen81 used asymmetric AC square wave with negative net DC component to deposit alumina particles coatings from aqueous suspensions. The obtained coatings were smooth and bubble- free. Yue et al.83 coupled a weak DC to a strong AC field to deposit Ag-sheathed Bi2Sr2CaCu2Oδ tapes with improved microstructures. The main characteristics of EPD under asymmetrical AC signals with net DC component are: i) In order to prevent formation of bubbles, if the applied current density increased, the frequency should also be increased.81 ii) Compared to pure DC, the obtained deposition rates are low, but the quality is better since the coatings have no incorporated gas bubbles. iii) If the employed AC field is stronger than the DC component, the produced microstructures should have high probability of orientation,83 thus a better quality. 3.2.3. Asymmetrical AC field with no net DC component. Fig. 2E depicts an example of the asymmetrical AC waveform with no net DC component. It will be noted that surface areas of the positive and negative half-cycles are equal. Thus, theoretically, no net DC component is induced (∫Edt = 0 over one period) to cause migration of the charged particle. Nevertheless, the difference in potential height and time duration (E–t) between the two half-cycles could cause the particle to migrate greater distance just like in DC fields, if the applied voltage is sufficiently high. http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (25 de 39) [31/01/2014 02:10:17 p.m.]
  • 26. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H For low electric field strengths, traditional electrophoresis theory assumes a linear dependence between the velocity of the particle motion, Veph, and the electric field strength, E, as illustrated in eqn (1). If the voltage is sufficiently high, this theory becomes non-linear and can be described by adding a second term with the cubic dependence on the electric field strength:20 Veph = μephE + μeph,3E3 (6) In other words, in the signal of Fig. 2E, during the weak voltage-pulse, the nonlinear component would be absent and only the linear one is present. The theory of non-linear or non-uniform electrophoresis was observed and theoretically described in many papers in the course of the past 35 years20,84–94 and the reason behind it is to do with the electrical double layer of the suspended charged particle. Stotz86 suggested that if the electric field is sufficiently strong, the electric double layer would completely be stripped off. Thus, the particle charge can directly be calculated by equating the Coulomb and Stokes forces. Recently, the theory of nonlinear electrophoresis was tested experimentally and found to successfully produce thick deposits of inorganic,95,96 organic–inorganic particles97 and enzymes and biological cells.24,28,29,98–100,103 Using asymmetrical triangular waves, Neirinck et al.95,96 deposited thick and uniform alumina coatings with higher green density from low aqueous conductivity suspensions at 50 Hz and 500 Vp–p. Green density can be defined as the ratio of the ceramic powder volume to the external volume of the deposit. If the green density is low, cracking during drying and/or sintering of the deposit occur because of the large change in the volume. Fig. 11 illustrates the shape of the triangular wave used for EPD and the resulting alumina deposit in comparison with a coating obtained using CDC. While using CDC from aqueous suspensions, a porous coating is formed; the deposit produced under asymmetrical AC waveform is non-porous and homogenous. The reason for that is to do with water electrolysis. http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (26 de 39) [31/01/2014 02:10:17 p.m.]
  • 27. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H Fig. 11 (A) One period of the applied asymmetric triangular AC signal and alumina deposits formed using 100 V DC for 1200 s (B) and 50 Hz and 500 Vp–p asymmetric AC field (C). Image reproduced from ref. 95 with permission of Elsevier. According to theoretical predictions, electrochemical reactions are suppressed using symmetric AC signals (Fig. 2C) if the frequency is sufficiently high because most of the electrochemical reactions are slow.20 Moreover, even when the frequency lies below the cut-off frequency of the electrochemical reaction, reaction products formed during the positive (or negative) part of the period are partly consumed when the signal is reversed during the rest of the period, thus lowering the reaction products. By contrast, when asymmetrical AC signals such as the triangular wave of Fig. 11 are used of which the integral over one period is zero, the difference in the voltage height and time duration (E–t) between the positive and the negative half-cycles will produce water electrolysis. The rate of electrolysis increases by lowering the frequency, elevating the voltage and the ionic conductivity of the suspension.101 However, compared to the electrolysis rates obtained by CDC, the rates under asymmetrical AC without net DC component are significantly low to yield large gas bubbles and damage of the deposited coating. It turns out that the conditions from which EPD is accomplished under asymmetrical AC without net DC component including aqueous solvents and low electrolysis rates are conditions suitable to deposit biomolecules such as enzymes and biological cells. Ammam and Fransaer24 demonstrated that using asymmetrical triangular waveform of Fig. 11, thick and active layers of glucose oxidase (more than 10 μm) could be deposited at 30 Hz and 160 Vp–p. Such thicknesses cannot be achieved by classical electrodeposition from either buffers27 or low conductivity solutions.49 This suggests that under asymmetrical waves, the enzymes migrate greater distance to http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (27 de 39) [31/01/2014 02:10:17 p.m.]
  • 28. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H reach the electrode and deposit. Also, 89 μm thick layers of biological cells, S. Cerevisiae, were deposited under the applied conditions of 30 Hz and 200 Vp–p for 30 min (Fig. 12B). By comparison, using symmetrical triangular AC waves without net DC component, only a monolayer of S. Cerevisiae can be formed (Fig. 12A). Fig. 12 SEM micrographs showing the morphology of deposited S. Cerevisiae cells layers using symmetrical triangular waveform for 30 min at 30 Hz and 200 Vp–p (A) and using asymmetrical triangular wave of Fig. 11(A) for 30 min at 30 Hz and 200 Vp–p (B). Part of the image reproduced from ref. 28 with permission of Elsevier. The main characteristics of EPD under asymmetrical AC waves without net DC component are: i) The deposition yield increases linearly with the polarization time for both inorganic ceramic materials95,96 and biochemical and biological species.24,28 ii) The deposition rates vary quasi-linearly with the applied amplitude then reach a saturation plateau,24,95 confirming in some sort that nonlinear mode of electrophoresis takes place at high voltages (eqn (6)). iii) With respect to frequency, the deposition yield increases with the frequency from 0–50 Hz, reaches a plateau95 then drops at elevated frequencies.24 This is understandable since if the frequency is changing faster, the particles will no longer follow the AC field because of their inertia. As a consequence, the particles oscillate in a single place and their net migration is significantly reduced. 4. Applications of films by EPD under PDC and AC In recent years, there has been a rising interest in nano and micro-structured materials because they usually exhibit novel and improved properties suitable for various applications. Compared to http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (28 de 39) [31/01/2014 02:10:17 p.m.]
  • 29. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H other deposition processes such as lithography, self-assembly, dip coating and spin coating, EPD technique offers the advantage of being versatile, cost saving and more importantly, allows deposition of high rates of particles in a controlled structural manner. Although, applications of films by EPD under CDC fields are wide and can be found in advanced ceramic materials, coatings for thin and thick films, multilayered composites, functionally graded materials, hybrid materials, self-supported components, micro-patterned assemblies, and nanotechnology.1 EPD under modulated electric fields, PDC and AC, offers new application perspectives such as in biotechnology. Because EPD can be accomplished from aqueous suspensions with low electrolysis rates under modulated electric fields, a variety of biochemical and biological species can be deposited to yield highly active layers suitable for a range of applications including biosensors, biofuel cells and bioreactors.24,28,29,75,98–104 Because EPD is an automated process, a variety of parameters such as voltage, frequency, concentration of the dispersed species and deposition time can be controlled to yield a better response under the optimized conditions. With regard to this, large number of biosensors with improved characteristics have recently been designed and manufactured by means of EPD under PDC and AC electric fields for detection of various analytes including glucose,24,49,99 lactose,98 glutamate100 and H2O2.103 Moreover, it is found that some biosensors are even dependable for determination of the analyte in real samples such as in milk and in blood.98,99 The latter is interesting considering the challenging aspects of the behavior of biosensors in real samples.105 By adding redox mediators, these electrodes have also been demonstrated to be useful for the manufacturing of glucose/O2 biofuel cells.104 Various microorganisms such as E. coli and S. Serevisiae cells have also been successfully deposited under modulated electric fields to form active monolayers29,75,102 and multilayers.28 In addition, some studies demonstrated that the viability of the deposited cells is even superior with respect to similarly treated free cells, thus improved bioreactors.28 Another important aspect of modulated electric fields over the classical CDC in EPD process is the control over the orientation of the particle during the deposition. The latter yields better ordered nano and micro-structures. In view of this, controlled zeolite microstructures can be formed on glassy carbon under PDC44 and, under AC fields, rod-shaped bacteria A. naeslundii75 as well as Bi2Sr2CaCu2Oδ tapes83 are observed to align parallel to the AC field. The well- organized and oriented deposited structures give rise to improved properties which is observed in many applications including superconductors,83 supercapacitors,97 field emission display devices http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (29 de 39) [31/01/2014 02:10:17 p.m.]
  • 30. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H based carbon nanotubes48 and sensitive ceramic gas sensors for CO and NO2 detection.77–79 Because PDC and AC generate low rate of water electrolysis and prevent coalescence between gas bubbles, high quality coatings useful for large range of applications such as ceramics and polymers can be produced.41–47,71,72,80,81,95,96 The smooth and non-porous texture of the coatings yields better anticorrosion properties. 5. Conclusions The reviewed literature revealed that EPD under modulated electric fields, PDC and AC, is a very promising process for the deposition of high quality coatings. From environmentally friendly aqueous solvents, it is shown that a variety of materials including, inorganic, organic–inorganic and biochemical and biological species can be deposited in controlled fashions. The formed deposits displayed improved characteristics compared to what can be obtained by classical CDC fields including smooth and bubble-free films, well oriented microstructures, and high activity biochemical and biological deposited species. In addition, because EPD under PDC and AC is automated, this leads to high reproducibility. The latter have been proven to lead to new applications particularly in biotechnology such as in biosensors (glucose, glutamate, hydrogen peroxide), biofuel cells and cell based bioreactors with improved characteristics. With respect to this, particular attention should be paid to deposition of biochemical and biological charged particles such as enzymes and biological cells because the conditions under which EPD can be performed are now suitable for these species. Given the great potential of EPD under modulated electric fields for manipulation and assembly of particles, further research and development of these processes will allow the understanding of the mechanisms behind the assemblies. Also, design and fabrication of 2D and 3D dimensional microstructures for novel generation of future advanced applications in nano and biotechnology. Acknowledgements The author would like to thank KU Leuven (GOA/08/007) and the Belgian Federal Science Policy Office (BELSPO) through the IUAP project INANOMAT (contract P6/17, Belgium) and Natural Sciences and Engineering Research Council of Canada, and the University of Ontario Institute of Technology (Canada) for their support. References http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (30 de 39) [31/01/2014 02:10:17 p.m.]
  • 31. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H 1. L. Besra and M. Liu, A review on fundamentals and applications of electrophoretic deposition (EPD), Prog. Mater. Sci., 2007, 52, 1–61 CrossRef CAS Search PubMed . 2. F. Begona and M. Rodrigo, EPD kinetics: A review , J. Eur. Ceram. Soc., 2010, 30, 1069– 1078 CrossRef Search PubMed . 3. I. Corni, M. P. Ryan and A. R. Boccaccini, Electrophoretic deposition: From traditional ceramics to nanotechnology, J. Eur. Ceram. Soc., 2008, 28, 1353– 1367 CrossRef CAS Search PubMed . 4. O. Van der Biest and L. J. Vandeperre, Electrophoretic deposition of materials, Annu. Rev. Mater. Sci., 1999, 29, 327–352 CrossRef CAS Search PubMed . 5. A. J. Bard, L. R. Faulkner, Electrochemical methods, Fundamentals and Applications, Wiley, NY, 2nd edn, 2001 Search PubMed . 6. H. von Both and J. Hauβelt, Ceramic microstructures by electrophoretic deposition of colloidal suspensions, in Proceedings on the electrophoretic deposition conference 2002, ed. A. R. Boccaccini, O. Vanderbiest, P. S. Nicolson and J. Talbot, Electrochemical Society Proceedings, 2002, vol. 21, pp. 78–85 Search PubMed . 7. M. S. Chronberg and F. Händle, Processes and equipment for the production of materials by electrophoresis ELEPHANT, Interceram, 1978, 27, 33–34 Search PubMed . 8. A. V. Kerkar, R. W. Rice, R. M. Spotnitz, Manufacture of optical ferrules by electrophoretic deposition, US Patent, 5 194 129 Search PubMed . 9. O. Sakurada, K. Suzuki, T. Miura and M. Hashiba, Bubble free electrophoretic deposition of aqueous zirconia suspensions with hydroquinone, J. Mater. Sci., 2004, 39, 1845– 1847 CrossRef CAS Search PubMed . 10. S. Lebrette, C. Pagnoux and P. Abelard, Fabrication of titania dense layers by electrophoretic deposition in aqueous media, J. Eur. Ceram. Soc., 2006, 26, 2727– 2734 CrossRef CAS Search PubMed . 11. R. Clasen, Forming of compacts of submicron silica particles by electrophoretic deposition, in Proceedings of the 2nd Int. Conf. on Powder Processing Science, pp. 633– 640, Deutsche Keramische Gesellschaft, Berchtesgaden ed. H. Hausner, G. L. Messing and S. Hirano, 1988, vol. 10, pp. 12–14 Search PubMed . 12. M. Ordung, J. Lehmann and G. Ziegler, Fabrication of fibre reinforced green bodies by electrophoretic deposition of silicon powder from aqueous suspension, J. Mater. Sci., 2004, 39, 889–894 CrossRef CAS Search PubMed . 13. J. Tabellion and R. Clasen, Electrophoretic deposition from aqueous suspensions for near- shape manufacturing of advanced ceramics and glasses-applications, J. Mater. Sci., 2004, http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (31 de 39) [31/01/2014 02:10:17 p.m.]
  • 32. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H 39, 803–811 CrossRef CAS Search PubMed . 14. C. Oetzel and R. Clasen, Manufacturing of zirconia components by electrophoretic deposition of nanosized powders, proceeding of the 27th Annual Cocoa Beach Conference on Advanced Ceramics and Composites: A, ed. W. M. Kriven and H. T. Lin, Ceramic Engineering and Science Proceedings, 2008, vol. 24, pp. 69–74 Search PubMed . 15. J. I. Hamagami, K. Kanamura, T. Umegaki, N. Fujiwara, M. Ito and S. Hirata, Direct deposition of alumina particles onto nonconductive porous ceramics by electrophoresis, in proceedings on the electrophoretic deposition conference 2002, ed. A. R. Boccaccini, O. Vanderbiest, P. S. Nicolson and J. Talbot, Electrochemical Society Proceedings, 2002, vol. 21, pp. 55–61 Search PubMed . 16. S. Novak, U. Maver, S. Peternel, P. Venturini, M. Bele and M. Gaberscek, Electrophoertic deposition as a tool for separation of protein inclusion bodies from host bacteria in suspension, Colloids Surf., A, 2009, 340, 155–160 CrossRef CAS Search PubMed . 17. P. Sarkar and P. S. Nicholson, Electrophoretic deposition (EPD): mechanisms, kinetics, and application to ceramics, J. Am. Ceram. Soc., 1996, 79, 1987– 2002 CrossRef CAS Search PubMed . 18. J. Lyklema, Water at interfaces: a colloid-chemical approach, J. Colloid Interface Sci., 1977, 58, 242–250 CrossRef CAS Search PubMed . 19. O. D. Velev and K. H. Bhatt, On-chip micromanipulation and assembly of colloids particles by electric fields, Soft Matter, 2006, 2, 738–750 RSC . 20. A. S. Dukhin and S. S. Dukhin, Aperiodic capillary electrophoresis method using an alternating current electric field for separation of macromolecules, Electrophoresis, 2005, 26, 2149–2153 CrossRef CAS Search PubMed . 21. M. H. Oddy and J. G. Santiago, A method for determining electrophoretic and electroosmotic mobilities using AC and DC electric field, J. Colloid Interface Sci., 2004, 269, 192–204 CrossRef CAS Search PubMed . 22. M. Zarbov, I. Schuster, L. Gal-Or Methodology for selection of charging agents for electrophoretic deposition of ceramic particles, in proceedings on the electrophoretic deposition conference 2002, ed. A. R. Boccaccini, O. Vanderbiest, P. S. Nicolson and J. Talbot, Electrochemical Society Proceedings, 2002, vol. 21, pp. 39–46 Search PubMed . 23. R. N. Basu, C. A. Randall and M. J. Mayo, Fabrication of dense zirconia electrolyte films for tubular solid oxide fuel cells by electrophoretic deposition, J. Am. Ceram. Soc., 2001, 1, 33–40 CrossRef Search PubMed . 24. M. Ammam and J. Fransaer, AC-electrophoretic deposition of glucose oxidase, Biosens. Bioelectron., 2009, 25, 191–197 CrossRef CAS Search PubMed . http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (32 de 39) [31/01/2014 02:10:17 p.m.]
  • 33. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H 25. J. Lyklema, H. P. Leeuwen and M. Minor, DLVO-theory, a dynamic re-interpretation, Adv. Colloid Interface Sci., 1999, 83, 33–69 CrossRef CAS Search PubMed . 26. B. Ferrari and R. Moreno, The conductivity of aqueous Al2O3 slips for electrophoretic deposition, Mater. Lett., 1996, 28, 353–355 CrossRef CAS Search PubMed . 27. N. Matsumoto, X. Chen and G. S. Wilson, Fundamental studies of glucose oxidase deposition on a Pt electrode, Anal. Chem., 2002, 74, 362–367 CrossRef CAS Search PubMed . 28. M. Ammam and J. Fransaer, Alternating current electrophoretic deposition of Saccharomyces cerevisiae cells and the viability of the deposited biofilm in ethanol production, Electrochim. Acta, 2010, 55, 3206–3212 CrossRef CAS Search PubMed . 29. B. Neirinck, L. Van Mellaert, J. Fransaer, O. Van der Biest, J. Anne and J. Vleugels, Electrophoretic deposition of bacterial cells, Electrochem. Commun., 2009, 11, 1842– 1845 CrossRef CAS Search PubMed . 30. N. Heavens, Electrophoretic deposition as a processing route for ceramics, in Advanced ceramic processing and technology, ed G. P. Binner, Noyes Publications, Park Ridge (NJ), USA, 1990, vol.1, pp. 255–283 Search PubMed . 31. R. W. Powers, The electrophoretic forming of beta-alumina ceramic, J. Electrochem. Soc., 1975, 122, 482–486 CrossRef Search PubMed . 32. Z. Jianling, W. Xiaohui and L. Longtu, Electrophoretic deposition of BaTiO3 films from aqueous suspensions, Mater. Chem. Phys., 2006, 99, 350–353 CrossRef Search PubMed . 33. H. C. Hamaker and E. J. W. Verwey, The role of the forces between the particles in electrodeposition and other phenomena, Trans. Faraday Soc., 1940, 35, 180–185 RSC . 34. F. Grillon, D. Fayeulle and M. Jeandin, J. Mater. Sci. Lett., 1992, 11, 272– 275 CrossRef CAS Search PubMed . 35. H. Koelmans, Suspensions in Non-Aqueous Media, Phillips Res. Rep., 1995, 10, 161– 193 Search PubMed . 36. D. De and P. S. Nicholson, Role of ionic depletion in deposition during electrophoretic deposition, , J. Am. Ceram. Soc., 1999, 8, 3031–3036 Search PubMed . 37. (a) W. D. Ristenpart, I. A. Aksay and D. A. Saville, Assembly of colloidal aggregates by electrohydrodynamic flow: kinetic experiments and scaling analysis, , Phys. Rev., 2004, E69, 0214051–0214058 Search PubMed ; (b) M. G. Song, K. J. M. Bishop, A. O. Pinchuk, B. Kowalczyk and B. A. Grzybowski, Formation of dense nanoparticle monolayer mediated by alternating current electric fields and electrohydrodynamic flows, http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (33 de 39) [31/01/2014 02:10:17 p.m.]
  • 34. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H J. Phys. Chem. C, 2010, 114, 8800–8805 CrossRef CAS Search PubMed . 38. Y. Solomentsev, M. Bohmer and J. L. Anderson, Particle clustering and pattern formation during electrophoretic deposition: A hydrodynamic model, Langmuir, 1997, 13, 6058– 6068 CrossRef CAS Search PubMed . 39. S. Ghosal, Fluid mechanics of electroosmotic flow and its effect on band broadening in capillary electrophoresis, Electrophoresis, 2004, 25, 214–228 CrossRef CAS Search PubMed . 40. D. C. Prieve, P. J. Sides and C. L. Wirth, 2D particle assembly of colloidal particles on a planar electrode, Curr. Opin. Colloid Interface Sci., 2010, 15, 160– 174 CrossRef CAS Search PubMed . 41. L. Besra, T. Uchikoshi, T. S. Suzuki and Y. Sakka, Pulsed-DC electrophoretic deposition (EPD) of aqueous alumina suspension for controlling bubble incorporation and deposit microstructure, Key Eng. Mater., 2009, 412, 39–44 CrossRef CAS Search PubMed . 42. L. Besra, T. Uchikoshi, T. S. Suzuki and Y. Sakka, Application of constant current pulse to suppress bubble incorporation and control deposit morphology during aqueous electrophoretic deposition (EPD), J. Eur. Ceram. Soc., 2009, 29, 1837– 1845 CrossRef CAS Search PubMed . 43. N. N. Naim, M. Kuwata, H. Kamiya and I. W. Lenggoro, Deposition of TiO2, nanoparticles in surfactant-containing aqueous suspension by a pulsed DC charging-mode electrophoresis, J. Ceram. Soc. Jpn., 2009, 117, 127–132 CrossRef Search PubMed . 44. B. Yu and S. B. Khoo, Controllable zeolite films on electrodes-comparing dc voltage electrophoretic deposition and a novel pulsed voltage method, Electrochem. Commun., 2002, 4, 737–742 CrossRef CAS Search PubMed . 45. N. M. Nazli, I. Motoyuki, K. Hidehiro and L. I. Wuled, Electrophoretic packing structure from aqueous nanoparticles suspension in pulse DC charging, Colloids and Surfaces, Colloids Surf., A, 2010, 360, 13–19 CrossRef Search PubMed . 46. L. Besra, T. Uchikoshi, T. S. Suzuki and Y. Sakka, Experimental verification of pH localization mechanism of particle consolidation at the electrode/solution interface and its application to pulsed DC electrophoretic deposition, J. Eur. Ceram. Soc., 2010, 30, 1187– 1193 CrossRef CAS Search PubMed . 47. M. N. Naim, M. Lijima, K. Sasaki, M. Kuwata and H. Kamiya, Electrical-driven disaggregation of the two-dimensional assembly of colloidal polymer particles under pulse DC charging, Adv. Powder Technol., 2010, 21, 534–541 CrossRef CAS Search PubMed . 48. C. Y. Hsiao, T. F. Chan, S. H. Lee, K. Cheng, Y. A. Li, L. J. Tsai, J. S. Fang and C. C. Kuo, Electrophoresis deposition method to fabricate CNT-FED cathode in water base http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (34 de 39) [31/01/2014 02:10:17 p.m.]
  • 35. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H solution, Dig. Tech. Pap. - Soc. Inf. Disp. Int. Symp., 2005, 36, 411– 413 CrossRef CAS Search PubMed . 49. M. Ammam and J. Fransaer, A study on electrodeposition of glucose oxidase from low conductivity solutions, Electrochim. Acta, 2010, 55, 9125– 9131 CrossRef CAS Search PubMed . 50. P. J. Sides and C. W. Tobias, A close view of gas evolution from the back side of a transparent electrode, J. Electrochem. Soc., 1985, 132, 583– 587 CrossRef CAS Search PubMed . 51. M. Ammam and J. Fransaer, Micro-biofuel cell powered by glucose/O2 based on electro- deposition of enzyme, conducting polymer and redox mediators: Preparation, characterization and performance in human serum, Biosens. Bioelectron., 2010, 25, 1474– 1480 CrossRef CAS Search PubMed . 52. N. G. Green, A. Ramos and H. Morgan, AC electrokinetics: A survey of sub-micrometre particle dynamics, J. Phys. D: Appl. Phys., 2000, 33, 632–641 CrossRef CAS Search PubMed . 53. J. A. Fagan, P. J. Sides and D. C. Prieve, Evidence of multiple electrohydrodynamic forces acting on a colloidal particles near an electrode due to an alternating current electric field, Langmuir, 2005, 21, 1784–1794 CrossRef CAS Search PubMed . 54. P. J. Sides, Electrohydrodynamic particles aggregation on an electrode driven by an alternating current electric field normal to it, Langmuir, 2001, 17, 5791– 5800 CrossRef CAS Search PubMed . 55. J. Kim, J. L. Anderson, S. Garoof and P. J. Sides, Effects of zeta potential and electrolyte on particle interaction on an electrode under AC polarization, Langmuir, 2002, 18, 5387– 5391 CrossRef CAS Search PubMed . 56. J. A. Fagan, P. J. Sides and D. C. Prieve, Vertical motion of a charged colloids particles near an AC polarized electrode with nonuniform potential distribution: Theory and experimental evidence, Langmuir, 2004, 20, 4823–4834 CrossRef CAS Search PubMed . 57. J. A. Fagan, P. J. sides and D. C. Prieve, Mechanism of rectified lateral motion of particles near electrodes in alternating electric fields below 1 kHz, Langmuir, 2006, 22, 9846– 9852 CrossRef CAS Search PubMed . 58. P. C. Y. Chen, Alternating current electrophoresis of human red blood cells, Ann. Biomed. Eng., 1980, 8, 253–269 CrossRef CAS Search PubMed . 59. B. K. Gale and M. Srinivas, Cyclical electrical field flow fraction, Electrophoresis, 2005, 26, 1623–1632 CrossRef CAS Search PubMed . 60. Z. R. Li, G. R. Liu, J. Han, Y. Z. Chen, J. S. Wang and N. G. Hadjiconstantinou, http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (35 de 39) [31/01/2014 02:10:17 p.m.]
  • 36. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H Transport of biomolecules in asymmetric nanofilter arrays, Anal. Bioanal. Chem., 2009, 394, 427–435 CrossRef CAS Search PubMed . 61. P. D. Grossman, J. C. Colburn, Capillary Electrophoresis: Theory and Practice, Academic Press, New York, 1992 Search PubMed . 62. W. B. Russel, D. A. Saville, W. R. Schowalter, Colloidal Dispersions, Cambridge University Press, 1995 Search PubMed . 63. P. F. Rider and R. W. O'Brien, The dynamic mobility of particles in a nondilute suspension, J. Fluid Mech., 1993, 257, 607–636 CrossRef CAS Search PubMed . 64. H. A. Pohl, The motion and precipitation of suspensions in divergent electric fields, J. Appl. Phys., 1951, 22, 869–871 CrossRef CAS Search PubMed . 65. H. A. Pohl, Dielectrophoresis, Cambridge University Press, 1978 Search PubMed . 66. T. B. Jones, Electromechanics of Particles, Cambridge University Press, New York, 1995 Search PubMed . 67. R. Pethig, Dielectrophoresis: Using inhomogeneous AC electrical fields to separate and manipulate cells , Crit. Rev. Biotechnol., 1996, 16, 331–348 CrossRef Search PubMed . 68. W. M. Arnold, H. P. Schwan and U. Zimmermann, Surface conductance and other properties of latex particles measured by electrorotation, J. Phys. Chem., 1987, 91, 5093– 5098 CrossRef CAS Search PubMed . 69. X. B. Wang, R. Pethig and T. B. Jones, Relationship of dielectrophoretic and electrorotational behavior exhibited by polarized particles, J. Phys. D: Appl. Phys., 1992, 25, 905–912 CrossRef CAS Search PubMed . 70. R. Hagedorn, G. Fuhr, T. Muller and J. Gimsa, Traveling wave dielectrophoresis of microparticles, Electrophoresis, 1992, 13, 49–54 CrossRef CAS Search PubMed . 71. (a) Making Rubber Objects From Dispersions by Electrophoretic Deposition in an Alternating Current, Dunlop Rubber Co. Ltd. and The Anode Rubber Co. Ltd.,1930, DE 587700 19331107 Search PubMed ; (b) Goodlass Wall and Co LTD., Electrophoretic deposition of resinous films on metallic objects, FR Pat, 1 409 893, 1969 Search PubMed ; (c) T. Sunamori, S. Obana, Electrophoretic Coating Process Using Alternating Current, JP 51123243 A 19761027 Search PubMed ; (d) T. Sunamori, S. Obana, Electrophoretic Coating of Substrates by Alternating Currents, 1976, JP 51055340 A 19760515 Search PubMed ; (e) T. Sunamori, Y. Obana, Alternating Current Electrophoretic Coating of Metal with Resins, 1976, JP 51086544 A 19760729 Search PubMed ; (f) T. K. Kokai, Electrophoretic Coating of Anodized Aluminum Substrates by Alternating Current, 1980, JP 55054596 A 19800421 Search PubMed . http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (36 de 39) [31/01/2014 02:10:17 p.m.]
  • 37. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H 72. R. Riahifar, B. Raissi, E. Marzbanrad and C. Zamani, Effects of parameters on deposition pattern of ceramic nanoparticles in non-unifrom AC electric field, J. Mater. Sci.: Mater. Electron., 2011, 22, 40–46 CrossRef CAS Search PubMed . 73. Z. R. Ul'berg, T. V. Kuznetsova and A. S. Dukhin, Electrophoretic dispersion deposition in external alternating electric field, Dopov. Akad. Nauk Ukr. RSR, Ser. B: Geol., Khim. Biol. Nauki, 1979, 11, 936–940 Search PubMed . 74. Y. Hirata, A. Nishimoto and Y. Ishihara, Forming of alumina powder by electrophoretic deposition, J. Ceram. Soc. Jpn., 1991, 99, 108–113 CrossRef CAS Search PubMed . 75. A. T. Poortinga, R. Bos and H. J. Busscher, Controlled electrophoresis deposition of bacteria to surface for the design of biofilms, Biotechnol. Bioeng., 2000, 67, 117– 120 CrossRef CAS Search PubMed . 76. A. R. Gardeshzadeh, B. Raissi and E. Marzbanrad, Deposition of multiwall carbon nanotubes using low frequency alternating electrophoretic deposition, Key Eng. Mater., 2009, 412, 83–86 CrossRef CAS Search PubMed . 77. A. R. Gardeshzadeh, B. Raissi, E. Marzbanrad and H. Mohebbi, Fabrication of resistive CO gas sensor based on SnO2 nanopowders via low frequency AC electrophoretic deposition, J. Mater. Sci.: Mater. Electron., 2009, 20, 127–131 CrossRef CAS Search PubMed . 78. E. K. Heidari, C. Zamani, E. Marzbanrad, B. Raissi and S. Nazarpour, WO3-based NO2 sensors fabricated through low frequency AC electrophoretic deposition, Sens. Actuators, B, 2010, B146, 165–170 CrossRef CAS Search PubMed . 79. E. K. Heidari, E. Marzbanrad, C. Zamani and B. Raissi, Nanocasting synthesis of ultrafine WO3 nanoparticles for gas sensing applications, Nanoscale Res. Lett., 2010, 5, 370– 373 CrossRef CAS Search PubMed . 80. R. Riahifar, E. Maezbanrad, B. R. Dehkordi and C. Zamani, Role of substrate potential on filling the gap between two planar parralel electrodes in electrophoretic deposition, Mater. Lett., 2010, 64, 559–561 CrossRef CAS Search PubMed . 81. A. Nold and R. Clasen, Bubbles free electrophoretic deposition shaping from aqueous suspension with micro point electrode, J. Eur. Ceram. Soc., 2010, 30, 2971– 2975 CrossRef CAS Search PubMed . 82. Y. Shindo, M. Nakamura and T. Tanaka, Alternating current electrophoretic coating process. III. Effect of substrate metals on the properties of coatings, Aruminyumu Hyomen Shori Kenkyu Chosa Hokoku, 1974, 91, 73–74 CAS Search PubMed . 83. C. F. J. Yue, D. Kumar and R. K. Singh, Fabrication of Ag-sheathed Bi-Sr-Ca-Cu-O thick http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (37 de 39) [31/01/2014 02:10:17 p.m.]
  • 38. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H films by a novel AC electric field assisted electrophoretic deposition method, Phys. C, 1999, 314, 291–298 CrossRef CAS Search PubMed . 84. S. S. Dukhin, A. K. Vidybida, A. S. Dukhin and A. A. Serikov, Aperiodic electrophoresis. Directed drift of disperse particles in a uniform, alternating anharmonic electric field, Kolloidn. Zh., 1988, 49, 853–857 Search PubMed . 85. S. S. Dukhin, B. V. Derjaguin, Electrophoresis, 1972, ch. 10, Nauka, Moscow, pp. 195– 213 Search PubMed . 86. S. Stotz, Field dependence of the electrophoretic mobility of particles suspended in low- conductivity liquids , J. Colloid Interface Sci., 1978, 65, 118– 130 CrossRef CAS Search PubMed . 87. S. S. Dukhin, T. S. Simonova and I. T. Gorbachuk, Physics of solid body, Bull. Kiev Pedagogical Institute, 1972, 113–123 Search PubMed . 88. P. S. Vincett, High-field electrophoresis of insulating particles in insulating liquids. I. An electrical transient technique for studying particle mobility, charge, degree of aggregation, adhesive forces, and high-field charging mechanisms, J. Colloid Interface Sci., 1980, 76, 83–94 CrossRef CAS Search PubMed . 89. P. S. Vincett, High-field electrophoresis of insulating particles in insulating liquids. II. A study of the basic transport mechanisms, including a novel space charge limited conduction process, J. Colloid Interface Sci., 1980, 76, 95–106 CrossRef CAS Search PubMed . 90. S. S. Dukhin, Electrophoresis at large peclet numbers, Adv. Colloid Interface Sci., 1991, 36, 219–248 CrossRef CAS Search PubMed . 91. N. A. Mishchuk and S. S. Dukhin, Electrophoresis of solid particles at large Peclet numbers, Electrophoresis, 2002, 23, 2012–2022 CrossRef CAS Search PubMed . 92. S. S. Dukhin, Electrokinetic phenomena of the second kind and their applications, Adv. Colloid Interface Sci., 1991, 35, 173–196 CrossRef CAS Search PubMed . 93. N. A. Mishchuk, S. S. Dukhin, in Interfacial Electrokinetics and Electrophoresis, ed. A. Delgado, Marcel Decker, New York/Basel, 2002, pp. 241–275 Search PubMed . 94. A. S. Dukhin, Biospecific mechanism of double layer formation and peculiarities of cell electrophoresis , Colloids Surf., A, 1993, 73, 29–48 CrossRef Search PubMed . 95. B. Neirinck, J. Fransaer, O. Van der Biest and J. Vleugels, Aqueous electrophoretic deposition in asymmetric AC electric fields (AC-EPD), Electrochem. Commun., 2009, 11, 57–60 CrossRef CAS Search PubMed . 96. B. Neirinck, J. Fransaer, J. Vleugels and O. Van der Biest, Aqueous Electrophoretic Deposition at High Electric Fields, Electrophoretic deposition: Fundamentals and http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (38 de 39) [31/01/2014 02:10:17 p.m.]
  • 39. Electrophoretic deposition under modulated electric fields: a review - RSC Advances (RSC Publishing) DOI:10.1039/C2RA01342H applications III Book Series: Key Eng. Mater., 2009, vol. 412, pp. 33–38 Search PubMed . 97. M. Ammam and J. Fransaer, Ionic liquid-heteropolyacid: Synthesis, characterization, and supercapacitor study of films deposited by electrophoresis, J. Electrochem. Soc., 2010, 158, A14–A21 CrossRef Search PubMed . 98. M. Ammam and J. Fransaer, Two-enzyme lactose biosensor based on β-galactosidase and glucose oxidase deposited by AC-electrophoresis: Characteristics and performance for lactose determination in milk, Sens. Actuators, B, 2010, B148, 583– 589 CrossRef CAS Search PubMed . 99. M. Ammam and J. Fransaer, Glucose microbiosensor based on glucose oxidase immobilized by AC-EPD: Characteristics and performance in human serum and in blood of critically ill rabbits, Sens. Actuators, B, 2010, B145, 46–53 CrossRef CAS Search PubMed . 100. M. Ammam and J. Fransaer, Highly sensitive and selective glutamate microbiosensor based on cast polyurethane/AC-electrophoresis deposited multiwalled carbon nanotubes and then glutamate oxidase/electrosynthesized polypyrrole/Pt electrode, Biosens. Bioelectron., 2010, 25, 1597–1602 CrossRef CAS Search PubMed . 101. M. Ammam and J. Fransaer, Effects of AC-electrolysis on the enzymatic activity of glucose oxidase, Electroanalysis, 2011, 23, 755–763 CrossRef CAS Search PubMed . 102. V. Brisson and R. D. Tilton, Self-assembly and two-dimensional patterning of cell arrays by electrophoretic deposition, Biotechnol. Bioeng., 2002, 77, 290– 295 CrossRef CAS Search PubMed . 103. M. Ammam and J. Fransaer, AC-electrophoretic deposition of metalloenzymes: Catalase as a case study for the sensitive and selective detection of H2O2, Sens. Actuators, B, 2011, 160, 1063–1069 CrossRef CAS Search PubMed . 104. . M. Ammam and J. Fransaer, Glucose/O2 biofuel cell based on enzymes, redox mediators, and Multiple-walled carbon nanotubes deposited by AC-electrophoresis then stabilized by electropolymerized polypyrrole, Biotechnol. Bioeng., 2012, 109, 1601, DOI:10.1002/bit.24438 . 105. G. S. Wilson and M. Ammam, In vivo Biosensors, FEBS J., 2007, 274, 5452– 546 CrossRef CAS Search PubMed . This journal is © The Royal Society of Chemistry 2012 http://pubs.rsc.org/en/content/articlehtml/2012/ra/c2ra01342h (39 de 39) [31/01/2014 02:10:17 p.m.]