Effect of the degree of imidization on the pretilt angle of nematic liquid crystal E7

Abstract

Currently, liquid crystal devices (LCD) dominate the flat panel display industry. The quality of the display is directly related to the alignment of LC molecules on the substrate. This alignment depends on the interfacial interaction between liquid crystals and an alignment layer. The interfacial interactions present are due to the effects of surface morphology generated by rubbing and the physiochemical interaction between the LC and the alignment layer.
Most displays require homogenous alignment of the LC molecules. It is said to be homogenous when the LC molecules lie parallel to the surface of the substrate. However, the LC molecules do not exactly lie parallel to the substrate, they make a small angle with the substrate called the pretilt angle. The pretilt angle between LC and polymer alignment layer strongly depends on the surface tension of the polymer layer. By controlling the polymerization reaction with curing time or with curing temperature, the surface tension of the polymer layer can consequently be controlled.
In this study, we investigate the effect of the degree of imidization of the polymer layer on the induced pretilt of nematic E7 liquid crystal. We find that as the degree of imidization is increased, the induced pretilt angles likewise increases before 'leveling off' at some point.