Abstract
Sum-frequency vibrational spectroscopy (SFVS) and second-harmonic generation (SHG) were used to probe the structures of rubbed surfaces of polyimide (PI) with and without side chains and the alignment of liquid crystal (LC) monolayers adsorbed on them. The SFVS spectra show clearly the presence of rubbing-induced anisotropy indicating the induced alignment of the PI backbones at the surface, but they hardly exhibit any rubbing-induced anisotropy. The results lead to the conclusion that while the PI backbones are aligned by rubbing, the orientation of alkyl side chains are hardy affected because they are projecting out normally from the surface with a broad orientational distribution. The SHG measurement indicates that the LC monolayers adsorbed on the polymer are more or less aligned along the rubbing direction. The order parameter of the LC monolayer on the rubbed PI with alkyl side chains is smaller than that on the PI without alkyl side chains.