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Que.: Describe the types of Liquid Crystals.

Ans.:

Types of Crystals: Types of crystals are described as belows:

1. Lyotropic Liquid Crystals

2. Thermotropic Liquid Crystals

3. Metallotropic Liquid Crystals


1. Lyotropic Liquid Crystals :

(i) A lyotropic liquid crystals consists of two or more components that exhibit-crystalline properties in certain concentration ranges.

(ii) In the lyotropic phases, solvent molecules fill the space around the compounds to provide fluidity to the system. In contrast to thermotropic liquid crystal, these lyotropic have another degree of freedom of concentration that enables them to induce a variety of different phases.

(iii) A compound that has two immiscible hydrophilic and hydrophobic parts within the same molecule is called an amphiphilic molecule.

(iv) Many amphiphilic molecules show lyotropic liquid-crystalline phase sequences depending on the volume balances between the hydrophilic part and hydrophobic part.

2. Thermotropic Liquid Crystals :

(i) Thermotropic phases are those that occur in a certain temperature range. If the temperature rise is too high, thermal motion will destroy the delicate cooperative ordering of the LC phase, pushing the material into a conventional isotropic liquid phase.

(ii) At too low temperature, most LC materials will form a conventional crystal. Many thermotropic LCs exhibit a variety of phases as temperature is changed.

(iii) Depending on the shape of liquid crystals they are of three types:


3. Metallotropic Liquid Crystals:


  1. Liquid crystal phases can also be based on low-melting inorganic phases like ZnCl, that have a structure formed of linked tetrahedra and easily form glasses. The addition of long chain slap-like molecules leads to a series of new phases that show a variety of liquid crystalline behaviour both as a function of the inorganic-organic composition ratio and of temperature. This class of materials has been named metallo-tropic.
  2. Thus a metallotropic liquid crystal consists of metal ions incorporated into the liquid crystals.