Orientations of side chains and adsorbed liquid crystal molecules on a rubbed polyimide surface studied by optical second harmonic generation

Surface second harmonic generation was used to obtain approximate orientational distributions of the side chains and the adsorbed liquid crystal (LC) molecules on a rubbed side-chain polyimide surface. Both the side chains and the LC molecules appear to be well aligned in the rubbing direction but tilted away from the surface in the antirubbing direction. The latter yields a negative pretilt angle in a homogeneously aligned LC film sandwiched between two such surfaces. The side chains and the LC molecules, however, have antiparallel orientations at the surface.