STUDY ON THE SURFACE ALIGNMENT OF NEMATIC LIQUID-CRYSTALS - TEMPERATURE-DEPENDENCE OF PRE-TILT ANGLES

A simple phenomenological theory is presented for the surface or interface of nematic liquid crystals in terms of the surface order parameter Q//i//j. The theory is based on the existence of an easy axis at the surface, so that the surface order parameter is not only a function of a director but also the easy axis. Taking into account the concept of an easy axis field, the temperature dependence of pretilt angle can be expresed both for the free surface and the interface between liquid crystals and solid substrate. Two typical experimental results of temperature dependent angle obtained by Bouchiat and Langevin-Cruchon, and Toda, Mada and Kobayashi are compared with the theory, and good agreements are obtained qualitatively between them.