Liquid crystals are a state of matter that have properties between those of a conventional liquid and solid crystal. They may flow like a liquid but their molecules can be oriented in a crystal-like way. There are different types of liquid crystal phases which can be distinguished by their optical properties when viewed under a polarized microscope. Liquid crystals can be divided into thermotropic, lyotropic, and metallotropic phases, with thermotropic and lyotropic phases consisting of organic molecules and exhibiting phase transitions depending on temperature and concentration. Examples of liquid crystals can be found naturally and in technologies like electronic displays.

1. Liquid CrystaLs(LC’s)
By:Mayank Pandey
VIT University, Vellore

2. Introduction

Liquid crystals (LCs) are matter in a state that has properties
between those of conventional liquid and those of solid crystal.

For instance, an LC’s may flow like a liquid, but its molecules
may be oriented in a crystal like way.

There are many different type of LC phases, which can be
distinguish by their different “optical properties” (such as
birefringence.
Which viewed under a microscope using a polarized light
source, different liquid crystal phases will appear to have distinct
textures.

3. The contrasting areas in the textures correspond to domain
where the LC molecules are oriented in different directions.

Within a domain , however the molecules are well ordered.
Imp:- LC material may not always be in LC phase (just as water
turns into ice or steam)


4. Phases of Liquid crystal
Liquid crystal can be divided into 3 phases:A)
B)
C)
Thermotropic phase
Lyotropic phase
Metallotropic phase
“ Thermotropic & lyotropic LC’s consists of organic molecule’s”

Thermotrpic LC’s exhibits a phase transition into the LC phase as
temperature is changed.

Lyotropic LC’s exhibits phase transition as a function of both
temperature & concentration of the LC molecules in a solvent( typical water).

Metallotropic LC’s are composed of both organic and inorganic molecules.
Here, LC transition depends not only on temperature &
concentration, but also on the inorganic- organic composition ratio.

5. Examples of LC’s
1) Examples of LC’s can be found both in natural world & in
technological application.
2) Most contemporary electronic displays uses liquid
crystals.
3) Lyotropic liquid crystalline phase are abundant in living
system.
4) Many protein and cell membranes are LC’s.
5) Other examples is solution of soap & various related
detergent, as well as tobacco mosaic virus.

6. Nematic Phases
The nematic liquid crystal phase is characterized by molecules
that have no positional order but tend to point in the same
direction (along the director). In the following diagram, notice tha
the molecules point vertically but are arranged with no particular
order.

7. Smectic state
1. The smectic state is another distinct mesophase of liquid crystal
substances.
2. Molecules in this phase show a degree of translational order not
present in the nematic. In the smectic state, the molecules maintain
the general orientational order of nematics, but also tend to align
themselves in layers or planes.
3. Motion is restricted to within these planes, and separate planes are
observed to flow past each other. The increased order means that
the smectic state is more "solid-like" than the nematic.