Liquid Crystals(LC’s)

By:-Mayank PandeyVIT University, Vellore

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.

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)

Phases of Liquid crystalLiquid crystal can be divided into 3 phases:-

A) Thermotropic phaseB) Lyotropic phaseC) 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.

Examples of LC’s1) 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.

Nematic PhasesThe 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 that the molecules point vertically but are arranged with no particular order.

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.

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