1. Design and Properties of Molecular Materials: Liquid Crystals
Third Year Course: CHM3T1
Special Chemical Topics
Weeks 12-22: Totally 11hrs
Totally 9 lectures and 1 hr Review
1 hr Workshop

2. Course Content
Thermotropic Liquid Crystals (3hrs)
Lyotropic Liquid Crystals (1hr)
Contemporary Research in Liquid Crystals (1hr)
Design, Synthesis, Properties and Applications of Liquid Crystalline Materials (3hrs)
Liquid Crystal Technology (LCT) (1hr)

3. Course Main Learning Objectives
What does the term Liquid Crystal Mean?
What is the molecular structure of a liquid crystal?
What is the bulk structure of a liquid crystal?
How do liquid crystals interact with light?
How do liquid crystals interact with electric fields?
How do liquid crystals interact with surfaces?
The Twisted Nematic liquid Crystal Display (TNLCD)

4. The University of Birmingham
Liquid Crystals Display In Our Everyday Life
Introduction To
Liquid Crystals
LCD (Liquid Crystal Display) is used as display panel of
calculators,
watches,
word-processors,
monitors,
Note PCs,
TVs, and
many household electric appliances.
With it's light weight, it has become a necessity for many mobile
items as dry batteries have become smaller and longer in life.
CHM3T1
Lecture-1
Dr. M. Manickam
School of Chemistry
The University of Birmingham

5. Outline of Lecture Introduction Historical background
Classification of Liquid Crystals
Examples of Liquid Crystals
Guide to the Nomenclature and General Definitions
References
Final Comments

6. Learning Objectives
After completing this lecture you should have an understanding of, and be able to demonstrate, the following terms, ideas and methods.
What are liquid crystals?
What does anisotropic mean?
What does mesophase mean?
The term mesogens.
The different types of liquid crystal and their arrangement

7. General Definitions
Liquid crystal state: symbol LC - A mesomorphic state having long range orientational order and either partial positional order or completed positional disorder.
Mesomorphic state: a state of matter in which the degree of molecular order is intermediate between the perfect three-dimensional, long-range positional and orientational order found in solid crystals and the absence of long-range
order found in isotropic liquids, gases and amorphous solids.
Liquid crystal: a substance in the liquid crystal state.
Mesophase or Liquid crystal phase: phase that does not possess long-range positional ordering, but does have long-range orientational order.
A phase occurring over a defined range of temperature or pressure or concentration within the mesomorphic state.
Mesogen (mesomorphic compound): A compound that under suitable conditions of temperature, pressure and concentration can exist as a mesophase.

8. Nomenclature Cr or C or K: crystalline phase N: nematic phase
S: smectic phase
n: director
N*: chiral nematic (cholesteric)
Tg : glass-transition temperature
I: isotropic
ND: nematic discotic phase
Colh: hexagonal discotic
TN-I for a nematic-isotropic
transition
Cr 34 N 56 I :designates a compound
melting at 34 0C into the nematic phase;
at 56 0C it changes into the isotropic
phase; normal behaviour

9. Anisotropic Liquid
An anisotropic liquid is a liquid, i.e. it has fluidity in much the same way as solvent such as water or chloroform has.
However, unlike water or chloroform where there is no structural ordering of the molecules in the liquid, molecules in anisotropic liquid are on average structural order relative to each other along their molecular axis.

10. What is a liquid crystal? 2. What is so special about liquid crystals?
A liquid crystals is a phase between solid and liquid states (phases)

11. Examples Example of a compound that shows no LCs phase
liquid water
0 degrees of
order
solid crystalline
water; 3- (dimensional)
degrees of order
gaseous water
0 degrees of
order
Example of a compound that shows LCs phases
Looks like milk
1 degree of order
3 degrees of order
0 degrees of order
0 degrees of order
3 degrees of order
in solid form
gooey material
2 degrees of order

12. Liquid Crystals (LCs) What is so special about liquid crystals?
LCs are orientationally ordered fluids with anisotropic properties
A variety of physical phenomena makes them one of the most interesting subjects of modern fundamental science.
Their unique properties of optical anisotropy and sensitivity to external electric fields allow numerous practical application.
Finally, liquid crystals are temperature sensitive since they turn
into solid if it is too cold, and into liquid if it is too hot.
This phenomenon can, for instance, be observed on
laptop screens when it is very hot or very cold.

13. 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

14. LCD: Multi Disciplinary Area of Research
Preparation of various
types of liquid
crystalline
compounds and
characterisation
Theory, law
and various
Physical
properties
LCD based
Technological
application
Device (manufactures)
Technological application

15. A Brief History of LCs
In 1888 the Austrian botanist Reinitzer found that cholesteryl benzoate showed two melting points each. The crystal of this material melted at oC into a cloudy fluid, which upon further heating to oC became clear.
What Reinitzer was observing was a liquid crystal phase.
Further, investigation were carried out by the German physicist O. Lehmann who
observed and confirmed, by using polarised optical microscope “crystal [which] can exist with a softness… that one could call them nearly liquid”.

16. A Brief History of LCs
In 1922 the French scientist G. Friedel produced the classification scheme of LCs, dividing them into three different types of mesogens (materials able to sustain mesophases), based upon the level of order the molecules possessed in the bulk materials.
Nematic (from the Greek word nematos meaning “thread”)
Smectic (from the Greek word smectos meaning “soap”)
Cholesteric (better defined as chiral nematic)
In the discovery of the most technologically and commercially important
class of liquid crystals to date: the 4-alkyl-4-’cyanobiphenyl of which an example
shown below.
This material which constitute the simple common displays found in calculators or mobile phones.

17. Types of LCs Different types of molecules can form LCs phases.
the common
structural feature is that these molecules are anisotropic:
one molecular axis is much longer Or wider than another one.
The two major categories are:
Thermotropic LCs, whose mesophase formation is temperature (T)
dependent
Lyotropic LCs, whose mesophase formation is concentration

18. Types of Liquid Crystals

19. Thermotropic LCs
The essential requirement for a molecule to be a thermotropic LC is a structure consisting of a central rigid core (often aromatic) and a flexible peripheral moiety (generally aliphatic groups).
This structural requirement leads to two general classes of LCs.
Calamitic LCs and
Discotic LCs
Both of which have molecular subclasses.

20. Calamitic LCs
Calamitic or rod-like LCs are those mesomorphic compounds that possess an elongated shape, responsible for the formanisotropy of the molecular structure, as the result of the molecular length (l) being significantly greater than the molecular breadth (b), as depicted in the cartoon representation in the figure.
Cartoon representation of calamitic LCs, where l>>b

21. Types of Calamitic LCs
Calamitic LCs can exhibit two common types of mesophases:
Nematic and
Smectic.

22. Nematic phase
The least ordered mesophase (the closest to the isotropic liquid state) is the nematic phase, where the molecules have only an orientational order.
The molecular long axis points on average in one favoured direction referred to an the director .
The classical examples of LC displaying a nematic mesophase in the cynobiphenyl
Molecules possess
Orientational order
Least ordered meso-
phase
The molecules are oriented on average, in the same direction referred to as the directed, with on positional ordering with respect to each other
Cartoon representation of N Phase.

23. Smectic phases
The next level of organisation is classified as smectic (S), where in addition to the orientational order the molecules possess positional order, such that the molecules organise in layered structures.
The S phase has many subclasses, of which are illustrated .
Molecules possess
Orientational order
Positional order
Layered structures
Cartoon representation of (a) the SA phases, and (b) the SC phase

24. Smectic phases
Example: 4,4’’’ – Bis-nonyloxy-[1,1’;1’’;4’’,1’’’] quaterphenyl (2)
exhibiting SA and SC phases.
The presence of such an extended aromatic core, characterised by a large pi system, is responsible for the establishment of lateral stacking interaction between adjacent molecule, resulting in a layered organisation (SA and SC)

25. Discotic LCs
Similarly to the calamitic LCs, discotic LCs possess a general structure comprising a planar (usually aromatic) central rigid core surrounded by a flexible periphery, represented mostly by pendant chains (usually four, six, or eight), as illustrated in the cartoon representation.
As can be seen, the molecular diameter (d) is much greater than the disc thickness (t), imparting the formanisotropy to the molecular structure.
Cartoon representation of the general shape of discotic LCs, where d >>t

26. Discotic LCs
In 1977, a second type of mesogenic structure, based on discotic (dis-shaped) molecular structure was discovered.
The first series of discotic compounds to exhibit mesophase belonged to the hexa-substituted benzene derivatives synthesised by S. Chandrasekhar et al
Molecular structure of the first series of discotic LCs discovered: the benzene hexa-n-alkanoate derivatives

27. Types of Discotic LCs
Discotic LCs, as well as calamitic LCs, can show several types of mesophases, with varying degree of organisation
The two principle mesophases are:
nematic discotic, and
columnar

28. Nematic Discotic LCs
Nematic discotic (ND) is the least ordered mesophase, where the molecules have only orientational order being aligned on average with the director as illustrated .
Least ordered mesophase
Molecules have only orientational
order
There is no positional order.
Cartoon representation of the ND
phase, where the molecule are
aligned in the same orientation, with
no additional positional ordering

29. Columnar phases
Columnar (Col) phases are more ordered. Here the disc-shaped cores have a tendency to stack one on the top of another, forming columns.
Arrangement of these columns into different lattice patterns gives rise to a number of columnar mesophases, namely columnar rectangular (Colr) and columnar hexagonal (Colh) in the fashion described in Figure.
Cartoon representation of (a) the general structure of Col phases, where the
molecules are aligned in the same orientation and, in addition, form columns,
(b) representation of Colr, and (c) representation of Colh.

30. Discotic Liquid Crystals
Molecular structure of some discotic mesogens
2,3,6,7,10,11-hexakishexyloxy-
triphenylene
Porphyrin metallomesogen
100 oC
70 oC
184 oC
273 oC

31. Polycatenar Liquid Crystals
Polycatenar mesogens represent a hybrid class of thermotropic LCs, which can be described with intermediate molecular features between classic rod-like and disc-like mesogens.
The central core of polycatenar LCs comprises a calamitic region, with half- discs on the extremities.
This hybrid molecular structure allows both calamitic and columnar phases to be generated, depending on the molecular structure of the compounds.
Polycatenar molecules possess a number of flexible alkyl chain substituents, which varies from two to six.

32. Metallomesogens
Metal containing liquid crystals are called metallomesogens.
First of all, the possibility to obtain mesomorphism in compounds that exhibit geometries which are forbidden for pure organic structures, i.e. squar planar, octahedral, etc.
Secondly, the possibility to find new technological applications induced by the presence of metal ions in the complexes such as colour, polarizability, paramagnetism, etc.
Moreover, the development of bimetallic mesogens constitutes a further step in the field of magnetic and conductive materials since these types of compounds can exhibit paramagnetism and/or mixed oxidation states properties.
Phthalocyanine
Porphyrins

33. Lyotropic LCs
Lyotropic LCs are two-component systems where an amphiphile is dissolved in a solvent. Thus, lyotropic mesophases are concentration and solvent dependent.
The amphiphilic compounds are characterised by two distinct moieties, a hydrophilic polar“ head” and a hydrophobic “tail”.
Examples of these kinds of molecules are soaps (Figure-a) and various phospholipids like those present in cell memberanes (Figure-b).
[a]
[b]

34. Suggestions For Further Reading
Bahadur, B., editor. Liquid Crystals: Applications and Uses. Volumes 1, 2, and 3. World Scientific Publishing, 1990.
Chandrasekhar, S. Liquid Crystals, 1 and 2nd edition. Cambridge University Press, 1992.
Collings, P. J., and M. Hird. Introduction to Liquid Crystals: Chemistry and Physics.
Collings, P. J., and J. S. Patel, editors. Handbook of Liquid Crystal Research. Oxford University Press, 1997.
R. J. Bushby and O. R. Lozman, Current Opinion in Colloid and Interface Science (2002) 7, 343 – 354.
S. Kumar, Liquid Crystals, (2004), 31, 1037 – 1059.

35. Final Comments
Any study of liquid crystals must concern itself with both the chemistry and physics of this state of matter.
The most important areas of liquid crystal chemistry are the relationship between molecular structure and the properties of the various liquid crystal phases, the many methods for synthesising liquid crystalline compounds and the behaviour of amphiphilic molecules and polymers that from liquid crystal phases.
Liquid crystal physics concentrates on the mechanical, electrical, magnetic, and optical properties of the various liquid crystalline phases, the different theoretical models that describe both liquid crystal phases and the transition between them, and the behaviour of liquid crystals in technical devices.