A study of the relation between surface alignment of polymers and liquid-crystal pretilt angle

摘要

Liquid-crystal molecules on a rubbed-polymer alignment layer are oriented at a polar angle tilted away from the surface, but the physical reason for this pretilt is not clearly understood. We have developed a new method to determine the three-dimensionally tilted direction of the polymer by precise measurement of the optical retardation. By using this method, we determined the inclination angle of the polymer molecules near the surface of the polymer as a function of rubbing strength. Three kinds of polymers were investigated, including one main-chain type (low pretilt) and two side-chain types (high-pretilt and homeotropic alignment). The mechanism of pretilt generation is determined by comparing the relation between the inclination angle of the polymers and the pretilt angle of the liquid crystals.