Alignment of Liquid-Crystals on Rubbed Polyimide Films Prepared from Various Precursor Polymers

For poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) and poly(4,4′-oxydiphenylene pyromellitimide) (PMDA-ODA) in films, surface topographies and molecular in-plane orientations were very sensitive to the precursor origins as well as the softbake and imidization processes. Poly(amic diethyl ester) precursor produced higher surface roughness and lower molecular in-plane orientation in the resultant polyimide than the corresponding poly(amic acid). Rapid softbake and imidization process caused relatively high surface roughness and low molecular in-plane orientation in the resultant film. Rougher surface in the film was more favorably rubbed by rubbing process, causing higher pretilt angle in liquid-crystal molecules in contact with the rubbed film.