Liquid crystals:

Liquid crystals are also used as selective phases. Liquid crystals are intermediate between the crystalline solids and normal istotropic liquids. They can exist in liquid crystal phase-smectic and nematic. The solid passes from smectic liquid phase to the nematic and finally to the ' normal' liquid phase as temperature is raised. A typical formula for a liquid crystal is:

where, R is CH₂   or n - C ₆ H₁₃ or n - C ₇ H₁₅

The liquid crystals display a selective affinity for linear molecules. They will retain p-disubstituted benzenes associative to o-and m-isomers.