The Relationship between Pretilt Angle of Liquid Crystal and Optical Anisotropy of Alignment Film

Abstract

We investigated the relationship between the pretilt of liquid crystal and the optical anisotropy of three kinds of polyimide films (PI-A, PI-B and PI-C) rubbed under various conditions. The optical anisotropy of the rubbed films was detected by reflection ellipsometry, and was characterized according to anisotropic dielectric constants, the tilt of the principal dielectric axis and the thickness of the molecular oriented layer. The optical anisotropy of the rubbed PI-A and PI-C films was largely dependent on the rubbing condition. A monotonic decrease in pretilt was observed as the difference between the ordinary and extraordinary dielectric constants of the molecular oriented layers. In the case of PI-B, the optical anisotropy is changed very little when rubbing conditions were changed. The correlation between the optical anisotropy in PI-B and pretilt was unclear. It was concluded that the influence of molecular orientation on pretilt is strongly dependent on the polyimide type.