Comparative study of anchoring strengths for photo- and rubbing-aligned liquid crystals on photoisomerizable polyimide alignment films

The high-electric-field technique was used to measure the out-of-plane (pol ar) anchoring strength at the interface between a nematic liquid crystal, p entylcyanobiphenyl (5CB), and a photosensitive polyimide (PI) alignment lay er possessing an azo group in the main chain. The anchoring energy of the p hotoaligned state was found to be rather strong, on the order of 0.1 mJ/m(2 ), being at least half of the anchoring energy on the rubbed surface of the same azo PI. The anchoring energy exhibited a conspicuous peak near the cl earing temperature of 5CB, particularly in the photoaligned system, indicat ing a significant role of molecular motion in anchoring behavior.