Effects of polyimide surface structure on liquid crystal alignment

Abstract

It is proposed that a liquid crystal (LC) pretilt angle is determined by three major factors which are anchoring, electronic and steric interactions between LC molecules and polyimide (PI) alignment layer (AL) surfaces. Flexible units of a polyimide, specially a diamine of the PI repeat unit, give a relatively large pretilt angle. Polar functionality at the AL surface lowers the pretilt angle while a bulky group(s) increases the pretilt angle. Rubbing induces microscopic molecular re-orientation so that polar or dipole functional groups at the surface are oriented outward.