4. 01/15/16
Liquid Crystal – a stable phase of matter
characterized by anisotropic properties
without the existence of a 3-dimensional
crystal lattice – generally lying between the
solid and isotropic (“liquid”) phase.
6. A fluid phase in which a liquid crystal flows and will take the shape of
its container. It differs from liquid that there are still some
orientation order possessed by the molecules
7. A phase that exists between solid and liquid
Discovered in 19th century when studying a cholesterol
derivative
8. Assuming that the direction
of preferred orientation in a
liquid crystal (LC) is ↑, this
direction can be
represented by an arrow,
called the director of the
LC.
Each molecule is
orientated at some angle to
the director.
9. Typical Representation of a LC Molecule
Mesogens
Note: these molecules possess
very strong dipole moment
10. The liquid crystal molecules prefer to align parallel to
each other because of the strong intermolecular
attraction (π-π interaction)
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Nematic, Smectic & Cholesteric
Anisotropic substances may go through one or several
Liquid Crystal Phases
12. Molecules in this
phase are long and
rod-like in shape.
They are free to
move in space.
13. This phase can be
reached at lower
temperatures than the
nematic phase.
Molecules align
themselves in layers.
(They are restricted to
their plane.)
More order and
higher viscosity
14. Molecules with intermolecular forces that favor alignment
between molecules at a slight angle to one another
The director is not fixed in space as in a nematic phase, it
rotates throughout the sample
15. If an electric field is
applied to a liquid
crystal the
molecules will align
in the same
direction as the
field.
16. Criteria for a Molecule being
Liquid Crystalline
• The molecule must be elongated in shape-
length should be significantly greater than its
width
• Molecule must have some rigidity in its central
region
• The ends of the molecule are somewhat
flexible
17. A side chain R, two or more
aromatic rings A and A’, connected
by linkage groups X and Y, and at
the other end connected to a
terminal group R’.
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