Part-1. Liquid crystal (Definition, example, properties, types) | ch#4 | 11th class Chemistry

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In this video I have discussed about the liquid crystal in 11th class Chemistry. i discussed about the following things such as Whenever we study the properties of crystalline solids, we come to know that the pure solids melt sharply. The temperature remains constant at the melting point until all the solid melts.
In 1888, Frederick Reinitzer, an Austrian botanist discovered a universal property. He was studying an organic compound cholesteryl benzoate. This compound turns milky liquid at 145°C and becomes a clear liquid at 179°C. When the substance is cooled, the reverse process occurs. This turbid liquid phase was called liquid crystal. Uptil now, it has been reported that, there are many crystalline solids which melt to a turbid liquid phase, before inally melting to a clear liquid. These turbid liquid phases can low as liquids.
They have the properties like liquids as surface tension, viscosity, etc. But it is very interesting to
know that the molecules of such turbid liquids possess some degree of order as well. It means that these turbid liquids resemble crystals in certain properties and the most important properties are
optical ones. These turbid liquids are hence called liquid crystals. So, a liquid crystalline state
exists between two temperatures i.e. melting temperature and clearing temperature. A
crystalline solid may be isotropic or anisotropic, but liquid crystals are always anistropic.
฀ ฀฀ ฀ ฀฀ Crystal Liquidcrystal Liquid ฀ ฀฀ ฀ ฀฀
From 1888 to until about 30 years ago, liquid crystals were largely a laboratory curiosity. But
now they have found a large number of applications.
Those substances which make the liquid crystals are often composed of long rod like molecules.
In the normal liquid phase, these molecules are oriented in random directions. In liquid crystalline
phase, they develop some ordering of molecules. Depending upon the nature of ordering, liquid
crystals can be divided into nematic, smectic and cholesteric.
The properties of liquid crystals are intermediate between those of crystals and isotropic
liquids. They have the luidity of the liquids and the optical properties of the crystals.

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