Orientation of Liquid Crystal Molecules on Side-Chain Polyimide Alignment Layer Studied by Second-Harmonic Generation Interferometry

Second-harmonic generation (SHG) interferometry has been applied to determine the phase of SHG from an SHG-active side-chain polyimide (PI) alignment layer with SHG-active liquid crystal molecules evaporated onto it. The phase difference between SH waves from the PI layer and from the PI layer with evaporated LC molecules monotonically increases with increasing evaporation time, while the SHG intensity increases after an inital decrease. These two facts indicate that LC molecules are adsorbed with an antiparallel polar orientation with respect to the polar side-chain orientation. The applicability of this method in studying the orientational relationship between an alignment layer and a LC monolayer is pointed out.