Unit 1- Class 2- Liquid Crystals (Classification of liquid crystals)

Classification of liquid crystals


Liquid crystals are classified into two main categories:
1. Thermotropic liquid crystals
2. Lyotropic liquid crystals


Thermotropic liquid crystals are those, which exhibit liquid crystalline properties as the temperature is varied. The liquid crystal to liquid transition and liquid-to-liquid crystal transitions of a mesogenic material are essentially reversible. The mesophase which are formed by both the heating and cooling cycles are thermodynamically stable are called enatiotropic phases. But in some compounds, their thermotropic phases appears only during the cooling phase from the isotropic phase, but not on the heating process. These mesophases, formed by the super cooling of the material below its melting point, are meta-stable and are called monotropic phases.


Thermotropic liquid crystals can exist in three phases

1. Nematic phase
2. Cholesteric or chiral nematic phase
3. Smectic phase

This will be discussed in our next class