Nematic Liquid Crystals

This chapter concerns with the structure and properties of thermotropic calamitic nematic liquid crystals (LCs). Three types of nematic phases are known: uniaxial nematic, biaxial nematic and twist-bend nematic. All these possess orientational order but differ in some characteristic features which are discussed in this chapter. The uniaxial and biaxial nematic phases are characterized by the symmetries T(3) x D∞h and T(3) x D2h, respectively. In the twist-bend nematic (NTB) phase which has been observed, in recent years, in achiral systems, the director has an oblique helicoidal structure. The basic aim of the present chapter is to introduce some of the important characteristic features of biaxial and twist-bend nematic phases. In case of uniaxial nematic phase, the structure–property relationship, characteristic features and theoretical development of nematic-isotropic (NI) transition, influence of external perturbation on the NI transition, elastic and dynamical properties have been discussed. We will be brief in these discussions.