MICROSCOPIC MOLECULAR-REORIENTATION OF ALIGNMENT LAYER POLYMER SURFACES INDUCED BY RUBBING AND ITS EFFECTS ON LC PRETILT ANGLES

The orientation of functional groups, side chains, and repeat units at the surface of a liquid crystal (LC) alignment layer (AL) polyimide w as changed by rubbing with a cotton velvet cloth. It was discovered th at rubbing induced polar functional groups and repeat units to reorien t out-of-the-plane of the surface, and it made nonpolar aliphatic side chains partially reorient inward, toward the bulk of the film. The po lar AL surface provided relatively small LC pretilt angles while polyi mides with long alkyl side chains gave relatively large LC pretilt ang les. The results suggest that LC pretilt angles are greatly affected b y bath electronic interaction and steric repulsion between LC molecule s and an alignment layer polyimide surface.