[Answered]What are liquid crystals? Discuss in brief the characteristic useful features of liquid crystals and their great range of applications in diverse fields.

Liquid crystals (LCs) are a state of matter which has properties between those of conventional liquids and those of solid crystals. For instance, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. LC materials may not always be in a liquid-crystal state of matter (just as water may turn into ice or water vapour).

Useful features:

1. By virtue of their fluid nature, LCs can be easily processed into thin films, yet they retain the optical properties of crystalline materials such as the ability to rotate the plane polarised light.
2. In addition, the orientation of the molecules in liquid crystal films can be modulated on a relatively short time scale using low electric field.
3. Liquid crystals reflect light with a wavelength proportional to the magnitude of pitch which is dependent upon temperature and colour.This is useful in accurately gauge temperature just by looking at the colour.
4. Polymers form an important subclass of liquid crystal materials and occur in nature as solutions of some biopolymers and are important in processing of advanced high-modulus engineering materials like Kevlar.

Applications of liquid crystals:

1. The temperature-dependent variation in the colour of liquid crystals has led to the use of these substances in the measurement of temperature gradients. Cholesteric liquid crystal substances, when applied to the surface of the skin, have been used to locate veins, arteries, infections, tumours and the fetal placenta which are warmer than the surrounding tissues.
2. Nematic liquid crystal are useful research tools in the application of magnetic resonance imaging (MRI).
3. Now a days liquid crystals are widely used in cosmetic industry in manufacturing of liquid crystal makeup removers, lipsticks and lip glasses containing liquid crystals. Liquid crystals are using extensively in pharmaceutical industries.
4. Liquid crystal displays are common in calculators, digital watches, television displays etc. Liquid crystals have also been used for novelty items such as toys and decorative materials.
5. Polyester liquid crystals were developed for fire resistant, and are used as coating for multi fibres, optical cables due to good surface roughness, low coefficient of friction.

Thus, liquid crystals because of their properties has immense applications in pharmaceutical industry, cosmetic industries etc. Due to its wide range of flexibility and applicability liquid crystals have a lot of potential application for which R&D is going on.