What are Liquid Crystals?

Mesophases (liquid crystals and plastic crystals) are a state of order between crystals and liquids. They have imperfect long range orders of orientation and/or position. Thus, the can be fluid like a liquid and they can have anisotropic properties like crystals. Whereas the plastic crystals have a predominating positional order, the liquid crystals have a predominating orientational order.

The main reasons for the formation of liquid crystalline phases are:

• a simple geometrical form of the molecule: rods, discs or ball, which allow a closer packing in a mesophase (monophilic liquid crystals).
  
• an intramolecular contrast, which cases microseparation of different parts of the molecules (amphiphilic liquid crystals).
  

The simplest liquid crystalline phases are the nematic phases, which have no positional order.

Smectic phases have layered structures.

The term liquid crystals covers a wide area of chemical structures, physical properties and technical applications.

Typical chemical structures are:

• cholesterol ester
• phenyl benzoates
• surfactants
• paraffines
• glyco lipids
• cellulose derivatives

• LCD displays (STN, FLC, TN, etc.)
• dyes (cholesterics)
• advanced materials (Kevlar, Vectra)
• membrans
• temperature measurement (by changing colors)
• solvents for GC, NMR, reactions, etc.
• effect colors