Chiral Nematic Liquid Crystals

Chiral nematic (or cholesteric) liquid crystals are of great interest due to their special self-assembled helical structure and selective light reflection properties. It exhibits a spontaneous helical structure with twist axis perpendicular to the local orientation and is also known as twisted nematic phase. The molecules are arranged in layers with their long axis parallel to the layer planes and each plane is rotated with respect to neighboring planes. The combination of order and mobility present in the system is responsible for the self organization. The present chapter is devoted to the discussion of characteristic features of twisted nematic phase, measurement of pitch and factors influencing it, external field dependence of structure and pitch, optical properties and existence of chiral nematic phase in living matter.