Effects of Rubbing and Temperature Dependence of Polar Anchoring Strength of Homogeneously Aligned Nematic Liquid Crystal on Polyimide Langmuir-Blodgett Orientation Films

The effect of rubbing on the polyimide (PI) Langmuir-Blodgett (LB) surface-alignment films has been successfully evaluated by observing the temperature dependence of the polar anchoring strength of nematic liquid crystal 4-cyano-4'-n-pentylbiphenyl (5CB). Upon rubbing, the PI-LB films showed a significant increase in the anchoring strength. The anchoring strength showed a nearly divergent decrease toward the clearing temperature, which is a manifestation of the diminished surface ordering, as previously pointed out for obliquely evaporated SiO films. Based on the van der Waals theory developed by Yokoyama et al. [J. Appl. Phys. 61 (1987) 4501], the intrinsic parts of the anchoring energy have been obtained as a function of temperature and found to undergo nearly one order of magnitude increase on rubbing. The polar anchoring energies for 5CB were strongly related to the surface order parameter on PI-LB films.