Unit 1- Class 4- Liquid Crystals (Classification of liquid crystals)

Discotic or columnar liquid phases
Liquid crystals formed by molecules, which have disc like or plate like structures are classified as discotic liquid crystals. The simplest discotic phase is also called the nematic discotic phase because there is oreintational order, but they lack positional order. There is random motion of the molecules but on an average the axis perpendicular to the plane of each molecule tend to orient along the director. In smectic discotic or columnar phase, in addition to the oreintational order present, most of the molecules tend to position themselves in columns. The columns are arranged in a hexagonal lattice resembling a set .


Chiral smectic
In a similar way to chiral nematics there are chiral forms of smectic phases. The tilted director rotates from layer to layer forming a helical structure.


Banana shaped liquid crystals
Apart from the cigar shaped molecules some more exotic shaped liquid crystals are also reported. Below figure illustrates the stacking of banana shaped liquid crystals.


In the next class we will discuss about various effects on liquid crystals