1. Liquid Crystals
Afia Riaz
Bs(hons) Chemistry

2. What are liquid crystals ?
and liquid state offrom organic compounds and is thought of as the phase of matter
Liquid crystals form a crystal.This phenomena was discovered in 1888 by
between the solid and liquid state of a crystal.This phenomena was discovered in
Austrian chemist Frederich Reinitzer Liquid
1888 by Austrian chemist Frederich Reinitzer
crystals form from organic compounds and is
thought o
f as the phase of matter between the solid and liquid state of a
crystal.This phenomena was discovered in 1888 by Austrian chemist
Frederich Reinitzer.
form from organic compounds and is thought of as the phase of matter
between the solid and liquid state of a crystal.This phenomena was
discovered in 1888 by Austrian chemist Frederich Reinitzer.
chemist Frederich Reinitzer.

3. • A liquid crystal is substance that exhibit one or
more ordered phases at a temperature above the
melting point of solids.
• Instead of passing directly from the solid to the
loquid phase when heated these substance pass
through an intermediate which has some of the
freedom of motion possessed by liquids.
• Due yo partial ordering liquid crystal may be very
viscous and possess intermediate properties.

4. •

5. • There are many different types of LC phases,
which can be distinguished by their different
optical properties.
• When viewed under a microscope using a
polarized light source, different liquid crystal
phases will appear to have distinct textures.
• Despite significant differences in chemical
composition, these molecules have some common
features in chemical and physical properties.

6. • Substances that form liquid crystal structures
are quite common. Approximately 0.5% of
known carbon compounds have liquid crystal
states.
• Cholesterol myristate changes from the solid
state to an intermediate state (cloudy liquid) at
71 C, and from the intermediate state to the
liquid state at 86 C

7. 4-Cyano-4'-pentylbiphenyl

8. p-azoxyanisol

9. Liquid crystal phases

10. Thermotropic liquid crystals
 Thermotropic phases are those that occur in a
certain temperature range.
 If the temperature rise is too high, thermal motion
will destroy the delicate cooperative ordering of
the LC phase, pushing the material into a
conventional liquid phase. At too low
temperature, most LC materials will form a
conventional crystal
 Many thermotropic LCs exhibit a variety of
phases as temperature is changed.

11. 1. Nematic phase
 One of the most common LC phases is the nematic.In a
nematic phase, the calamitic or rod-shaped organic
molecules have no positional order, but they self-align to
have long-range directional order with their long axes
roughly parallel. Thus, the molecules are free to flow.
 Nematics have fluidity similar to that of ordinary
(isotropic) liquids but they can be easily aligned by an
external magnetic or electric field.

12. 2.Smectic phases
• The smectic phases, which are found at
lower temperatures than the nematicform
• well-defined layers that can slide over one
another in a manner similar to that of soap.
The smectics are thus positionally ordered
along one direction.
• More order and higher viscosity

13. 3.Blue Phases
• Liquid crystal 'blue phases' are highly fluid
self-assembled three-dimensional cubic defect
structures that exist over narrow temperature
ranges in highly chiral liquid crystals
• It was theoretically predicted in 1981 that
these phases can possess icosahedral
symmetry similar to quasi crystals.

14. • In May 2008, the first Blue Phase Mode LCD
panel had been developed

15. Lyotropic liquid crystals
• A lyotropic liquid crystal consists of two or
more components that exhibit liquid-
crystalline properties in certain concentration
ranges. In the lyotropic phases, solvent
molecules fill the space around the
compounds to provide fluidity to the system

16. Amphiphilic molecule
• A compound, which has two immiscible
hydrophilic and hydrophobic parts within the
same molecule, is called an amphiphilic
molecule. Many amphiphilic molecules show
lyotropic liquid-crystalline phase sequences
depending on the volume balances between
the hydrophilic part and hydrophobic part.
• Soap is an everyday example of a lyotropic
liquid crystal.

17. Biological liquid crystals
• Lyotropic liquid-crystalline phases are
abundant in living systems,
• biological membranes and cell
membranes are a form of liquid crystals
• For instance, the concentrated protein
solution that is extruded by a spider to
generate silk is, in fact, a liquid crystal
phase.
• DNA and many polypeptides can also
form LC phases

18. Uses of Liquid Crystals
• Flat screen television
• Wristwatches
• Laptop screens
• Digital clocks
• Thermometers
• Switchable windows

19. Conclusion
• We know today that many chemical compounds
can exist in the liquid crystal state, such as
cholesteryl benzoate. the world can focus on
ways to make this product useful in society. Over
the last century many applications such as the
detection of hot points in microcircuits, the
findings of fractures or tumors in humans and the
conversion of infared images have become
accessible due to the understanding of pitch in a
liquid crystal