This document discusses liquid crystals, their properties, types, and applications. It describes how liquid crystals have properties between solids and liquids, with some degree of molecular order. The main types discussed are thermotropic and lyotropic liquid crystals. Thermotropic liquid crystals change phase based on temperature, while lyotropic crystals depend on temperature, concentration, and solvent. Common applications mentioned include digital watches, phones, displays, and electronic devices that take advantage of liquid crystals' response to electric fields.

2. Liquid Crystals and their Applications
Muhammad Minhas Azeem
Roll No 7616
Govt College University Faisalabad
Department of Applied Chemistry

3. Learning Objectives

4. States of mattters
1: Solid
2 : Liquid
3: Gass
4:Liquid crystals
1 :Solid
o All Soilds have fix shape, fix
volume, ductile and high melting
and boiling point.
oIt is due to solids have high
attrective forces among the atoms
and molecules which holds the
atom together.
SiO² Quartz

5. Liquid Stucture of liquid molecules
o Attractive forces between the
molecules is weak as compared
to the soild but strong as compair
to gass.
o The molecules of liquids have
more empty spaces as compair to
the soild , move aroud with each
other but molecules remain close
to each other so fluid donot have
fix shape and adapted the shape
of container.

6. Gas Stucture of gas molecules
o Gases have less attractive forces
among the molecules is weak.
o The molecules are faraway from
each.
o Gases move randomly so the
molecules of gass will expand
and fill the container.

7. Liquid Crystals
What is a liquid crystal?
What is so special about liquid crystals?
o A liquid crystals is a phase between solid and liquid states(phases)
Solidify
Melt
Liquid Crystal
Intermediate
Phase
Heat
Cool
Heat
Cool

8. Examples
Example of a compound that shows no LCs phase
heat heat
Ice Cube Water Steam
solid crystalline
water; 3- (dimensional)
degrees of order
liquid water
0 degrees of
order
gaseous water
0 degrees of
order
Example of a compound that shows LCs phases
Crystals of a solid
organic compound
Nematic liquid
crystals phase
Isotropic
liquid
Crystals of a solid
organic compound
Smectic liquid
crystal phase
Isotropic
liquid
heat heat
heat heat
3 degrees of order
Looks like milk
1 degree of order
0 degrees of
order

9. Phase
change

10. A Brief History of LCs
Liquid crystals was discoverd by Reinitzer and Lehmann in 1888.
cholesteryl benzoate showed two melting points each. The
crystal of this material melted at 145.5 oC into a cloudy fluid,
which upon further heating to 178.5 oC became clear
Cholesteryl
heat heat
145.5 0C 178.5 0C
benzoate Lehmann observed by using polarised optical microscope “and
observed crystal that were nearly liquid
O
O
R
FLEXIBLE RIGID FLEXIBLE
O
* * * *
*
*
*
*
R
O

11. History
In 1973 the discovery of the most technologically and commercial
important class of liquid crystals , 4-alkyl-4-’cyanobiphenyl.This
material found in calculators or mobile phones
NC C5H11
24oC 35oC
K N I
Reinitze

12. LCD: Multi Disciplinary Area of Research
Physicist
Electrical&
Electronic
Engineering
Organic and
Material
Chemists Theory, law
and various
Physical
properties
Device (manufactures)
Technological application
Preparation
of various
types of liquid
crystalline
compounds
and
characterisati
on

13. Crystals vs Liquid Crystals
o A crystal is a highly ordered structure which
possesses long-range positional & orientational order
o For many substances these two types of order are
destroyed simultaneously when the crystal melts to
form a liquid
o For some substances, these orders are destroyed in
stages. These are liquid crystals

14. Properties of liquid crystals
o Liquid crystal can flow like a liquid, due to loss of
positional order
o Liquid crystal is optically birefringent, due to its
orientational order
o Transition from crystalline solids to liquid crystals
caused by a change of temperature – gives rise to
THERMOTROPIC liquid crystals
o Substances that are most likely to form a liquid crystal
phase at a certain temperature are molecules that are
ELONGATED & have some degree of RIGIDITY

15. Typical chemical structures
Cholesterol ester
Phenyl benzoates
Surfactants such as
polyethylene-oxides,
alkali soaps, ammonium
salts, lecithin
Paraffins
Glycolipids
Cellulose derivatives

17. Types of Liquid
Liquid crystals
Lyotropic Thermotropic
Calamitic Polycatenar Discotic Banana-shaped
Nematic (N)
Smectic (S)
Nematic Discotic(ND)
Columnar (Col)

18. Benzene-hexa-n-alkanoate derivatives
disk-like molecules
banana-shaped
calamitic LCs

19. Comparision betweenThermotropic and Lyotropic
o THERMOTROPIC
o Absence of solvent
o Rigid organic molecules
o Depends on Temperature
o Structures:
o Smectic
o Nematic
o Cholesteric
LYOTROPIC
o In solvent
o Surfactants
o Depends on
Temperature,
Concentration, salt,
alcohol
o Structures:
 Lamellar
 Hexagonal etc

20. LYOTROPIC LCs
Lyotropic LCs are two-component
1: Hydrophilic polar“ head
2: Hydrophobic “tail
Examples
 molecules of soaps
 phospholipids (present in cell memberanes)

21. LYOTROPIC LCs

22. As temperature increases…
o The first liquid crystal phase is the smectic A, where
there is layer-like arrangement as well as translational and
rotational motion of the molecules.
o A further increase in temperature leads to the nematic
phase, where the molecules rapidly diffuse out of the
initial lattice structure and from the layer-like arrangement
as well.
o At the highest temperatures, the material becomes an
isotropic liquid where the motion of the molecules
changes yet again.

23. The Arrangement of Molecules in the Nematic, Smectic, and
Cholesteric Liquid Crystal Phases

24. Stuctural phases of liquid crystal
Nematic
o Nematic drived from
the Greek word, ‘nema’’
which means "thread".
o No possitional order
o Molecules in same direction
o When temperatures is incrase
molecules will be allign
immediately
o In nematic crystal phase
molecules are arranged
paralell

25. Nematic liquid crystals are widely used in electro-optic
display devices
The classical examples of LC displaying a nematic mesophase
in the Cynobiphenyl
R CN

26. Cholesteric
o The first liquid crystal Cholestericthat was observed
through a polarising microscope is cholesteryl benzoate.
Thus, CHOLESTERIC liquid crystal OR chiral nematic
liquid crystal
 E.g. cholesteryl benzoate: LC 147C, isotropic 186C
o Cholesteric liquid crystals have great potential uses as
 sensors
 Thermometer
 fashion fabrics that change colour with temperature
 display devices

27.  In CHOLESTERIC phase, there is orientational order & no
positional order, BUT, director is in HELICAL ORDER.
o The structure of cholesteric depends on the PITCH, the
distance over which the director makes one complete turn
o One pitch - several hundred nanometers
o Pitch is affected by:-
 Temperature
 Pressure
 Electric & magnetic fields

28. SMECTIC
o SMECTIC phase occurs at temperature below
nematic or cholesteric
oMolecules align themselves approx. parallel & tend
to arrange in layers
o Not all positional order is destroyed when a
crystal melts to form a smectic liquid crystal
o Chiral smectic C liquid crystals are useful in LCDS

29. Smectic
o SMECTIC phase occurs at temperature
below nematic or cholesteric
o Molecules align themselves approx. parallel
& tend to arrange in layers
o Chiral smectic C liquid crystals are useful in
LCDS
Eample: 4,4’’’ – Bis-nonyloxy-[1,1’;1’’;4’’,1’’’]
quaterphenyl (2)

30. LIQUID CRYSTAL POLYMERS
o When liquid crystal polymers solidify, the liquid
crystal structure ‘freeze in’
o This results in materials of high tensile strength & in
some cases unusual electro-optical behaviour
o E.g. Kevlar aramid fibre – bullet-proof vest & airplane
bodies (aromatic polyamide)

31. Technological Application
Where are liquid crystals used?
 Liquid crystals can be found in the following devices:
 Digital watches
 Pocket TVs
 Gas pumps
 Parking meters
 Telecommunications
 Cell phones and pagers
 High-speed computing
 Digital signs
 Electronic games
 Personal digital assistants
 Electronic books
 Calculators
 Digital cameras and camcorders
 Fishfinders
 Thermometers

32. Applications
Construction of LCD

33. 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.

34. References
1: P.G de Gennes, Port.j , 2010 “The Physics of Liquid Crystals”, ref 5.
2: M. J. Stephen, Excellent review of basic properties
3: J. P. Straley “Physics of liquid crystals”, Ref. [2].
4: D. Fincham, rotational motion of linear molecules, 1984 , 47–48.
5: http://www.slideshare.net/Nawarajintermediate/liquid-crystal-and-its-application#
6: Stegemeyer H, Blumel T, Hiltrop K, Onusseit H and Porsch F, Liq. Cryst. 1986,1-28.
7: Tanimoto K and Crooker P,1985, Phys. Rev. A 32 1893-5.
8: Tsvetkov V, Acta Physicicochim (USSR) , 1942 (16- 132).
9: van der Meer B Wand Vertogen G, Phys. Lett, 1976. 59A( 279-81).
10: Wright D C and Mermin N D, Phys. Rev, 1985. A 31 3498-500.
11:Thoen J. 1988 Phys. Rev. A 37 1754-9
12 Tsvetkov V 1942 Acta Physicicochim (USSR) 16 132
13 Tanimoto K and Crooker P P 1984 Phys. Rev. A 29 1566-7 13 Tanimoto K, Crooker P P
and Koch G C 1985 Phys. Rev. A 32 1893-5