2. Emulsions
Emulsion, in physical chemistry, mixture of two
or more liquids in which one is present as
droplets and distributed throughout the other.
At least 2 phases:
Disperse or internal phase
Continuous or external phase.
3. 3
Emulsions
A
B C D
A.: Two immiscible liquids not emulsified
B. An emulsion of phase B dispersed in Phase A
C. Unstable emulsion slowly separates.
D. The emulsifying agent ( black film) places it self on the interface between phase A
and phase B and stabilizes the emulsion.
Phase A
Phase B
8. Identification test for Emulsions:
1) Dye Test
2) Dilution Test
3) Electrical conductivity Test
4) Fluorescence Test.
5) Cobalt Chloride Test.
By using Naked eye, it is very difficult to differentiate between
o/w or w/o emulsions. Thus, the following methods have been
used to identify the type of emulsions.
9. 1) Dye TEST:
Water-soluble dye will dissolve in the
aqueous phase.
Oil-soluble dye will dissolve in the oil
phase.
Microscopic View
Oil-soluble dye (e.g. Scarlet) Water-soluble dye (e.g. Amaranth dye)
O/W W/OO/WW/O
10. 2) Dilution test:
Based on the solubility of external phase of
emulsion.
O/W emulsion can be diluted with water.
W/O emulsion can be diluted with oil.
Few drops
of emulsion
Few drops
of water Water distribute
uniformly
Water separate
out as layer
O/W emulsion
W/O emulsion
11. 3) Electrical Conductivity test:
As we know water is good conductor of
electricity whereas oil is non-conductor.
Therefore, continuous phase of water
runs electricity more than continuous
phase of oil.
Electrode
Bulb
Emulsion
Bulb glows with O/W
Bulb doesn’t glow
with W/O
12. 3) Fluorescence test:
Oils give fluorescence under UV light,
while water doesn’t.
Therefore, O/W emulsion shows spotty
pattern when observed under UV.
while W/O emulsion fluoresces.
13. 4) Cobalt Chloride test:
Principle:
Cobalt Chloride solution is used for
identification of Emulsion. It is water
soluble so it changes colour when
encountered by O/W emulsion.
Procedure:
Filter paper is Dipped in Emulsion.
Filter paper changes its color from blue to
Pink
14. Theories of Emulsification:
1) Surface Tension Theory:
- lowering of interfacial tension.
2) Oriented-Wedge Theory:
- mono molecular layers of emulsifying
agents are curved around a droplet of the
internal phase of the emulsion.
3) Interfacial film theory:
- A film of emulsifying agent prevents the contact
and coalescing of the dispersed phase.
16. Emulsifying Agents:
It is a substance which stabilizes an emulsion .
Pharmaceutically acceptable emulsifiers must also :
be stable .
be compatible with other ingredients .
be non – toxic .
possess little odor , taste , or color .
not interfere with the stability of efficacy of the
active agent .
18. Methods of Preparation of Emulsions:
1) Continental or Dry Gum Method:
"4:2:1" Method
4 parts (volumes) of oil
2 parts of water
1 part of gum
2) English or wet Gum Method:
4 parts (volumes) of oil
2 parts of water
1 part of gum
19. 3) Bottle or Forbes Bottle Method:
useful for extemporaneous preparation of
emulsion from volatile oils or oleaginous
substance of low viscosity.
powdered acacia
+ Dry bottle
2 parts of oil
This method is not suitable for viscous oils (i.e.
high viscosity oil).
20. Emulsion stability ( Instability) -
Types
• Physical instability
• i. Flocculation
• Ii. Creaming or sedimentation
• iii. Aggregation or coalescence
• Iv. Phase inversion
22. Advantages of Emulsions:
Mask the unpleasant taste O/W is convenient means of oral
administration of water-insoluble liquids.
Oil-soluble drugs can be given parentrally in form of oil-in
water emulsion. (e.g Taxol).
Emulsion can be used for external application in cosmetic
and therapeutic Application because of Better and faster
absorption.
Sustained release medication.
Nutritional supplement.
Inert and chemically non-reactive.
Reasonably odorless and cost Effective.
23. disadvantages of
Emulsions:
Emulsions are thermodynamically unstable
and have short shelf-life.
Improper formulation of emulsions leads to
creaming and cracking of emulsion.
Improper selection of emulsifying agent leads
to phase inversion and some times it may also
lead to cracking.
24. Emulsions encountered in everyday life!Emulsions encountered in everyday life!
Metal cutting oils Margarine Ice cream
Pesticide Asphalt Skin cream
Stability of emulsions may be engineered to vary fromStability of emulsions may be engineered to vary from
seconds to years depending on applicationseconds to years depending on application
EMULSION STABILITY ( INSTABILITY)
Physical stability :
The term emulsion stability refers to the ability of an emulsion to resist changes in the properties over time. , the more stable the emulsion, the more slowly its properties change .
Stability ( Instability) of the emulsion is related to four major phenomenon :
Flocculation
Creaming or sedimentation
Aggregation or coalescence
Phase inversion
Flocculation :
Flocculation is defined as the association of particle within an emulsion to form large aggregates. However these aggregates can easily be redispersed upon shaking. It is considered as a precursor to the irreversible coalescence. It differs from coalescence mainly in that interfacial film and individual droplets remain intact. Flocculation is influenced by the charges on the surface of the emulsified globules. The reversibility of flocculation depends upon strength of interaction between particles as determined by
a the chemical nature of emulsifier,
b the phase volume ratio,
c. the concentration of dissolved substances, specially electrolytes and ionic emulsifiers.
ii. Creaming and sedimentation :
The upward or down ward movement of dispersed droplets is termed creaming or sedimentation respectively. In any emulsion, creaming or sedimentation takes place depending on the densities of disperse and continuous phases. Creaming or sedimentation is undesirable as it may lead to coalescence.
Factors affecting rate of creaming :
Rate of creaming is governed by Stoke’s law. As per Stoke’s law
=2r 2(ρ1 - ρ2 ) g / 9η
υ = rate of creaming or sedimentation
r = radius of droplets of dispersed phase
ρ1 , ρ2 = density of dispersed and continuous phase respectively
g = gravitational rate constant
η = viscosity of continuous phase.
Droplet size :
As per Stoke’s law, rate of creaming is directly proportional to the square of radius or diameter of the droplet size. Smaller is the diameter of the droplet, lesser will be the rate of creaming. So reduction in droplet size helps in reducing creaming or sedimentation.
Difference in densities of dispersed and continuous phase :
As per Stoke’s law no creaming is possible if densities of the two phases are equal. So Creaming can be avoided by adjusting the density of dispersed phase.
Viscosity of the continuous phase :
As per Stoke’s law, rate of creaming is inversely proportional to viscosity of the continuous phase. So increase in viscosity of the continuous phase by adding thickening agents can reduce the rate of creaming.
Factor affecting viscosity of Viscosity :
Viscosity of continuous phase : Is directly proportional to the viscosity of continuous phase. .Clays and gums increase the viscosity of continuous phase. For w/o emulsions addition of polyvalent metal soaps or use of high melting waxes and resins in the oil phase can be used to increase the viscosity.
Volume of internal phase : Depends upon the volume of internal phase. More the volume of internal phase greater is the viscosity.
Particle size of dispersed phase : On the particle size of dispersed phase Smaller the globule size, more will be the viscosity. That is why emulsion stability can be improved by reduction in globule size.
iii.Coalescence (Cracking ):
It is the process in which the emulsified particles join to form larger particles. The major factor which prevents coalescence is the mechanical strength of electrical barrier. That is why natural gums and proteins are so useful as auxiliary emulsifiers when used at low level , but can even be used a primary emulsifiers at high concentration.
Reasons for( Coalescence) cracking :
Globule size : If globule size is big, ( more than 1-3 µm), emulsion may first cream and then crack. A homogenizer can reduce the size of globules.
Storage Temperature : Extremes of temperature can lead to cracking. When water freezes, it expands , so undue pressure is expected on dispersed globules and the emulsifying film., which may lead to cracking. On the other hand, increase in temperature decreases the viscosity of the continuous phase and disrupts the integrity of interfacial film. An increasing number of collisions between droplets will also occur, leading to increased creaming and cracking.
Changes which affect the interfacial film : These may be physical, chemical or biological effects.
Addition of a common solvent.
Microbial contamination may destroy the emulsifying agent.
Addition of a emulsifying agent of opposite nature for example cationic to anionic.
Incorporation of excess disperse phase : Increasing the quantity of continuous phase will increase the concentration of globules and lead to their
Chemical instability ( Stability )
This may be due to
Oxidation
Hydrolysis
Microbial growth.