Electric force microscopy study of the surface electrostatic property of rubbed polyimide alignment layers

Two polyimides were synthesized for use as alignment layers. The pretilt an gles of the liquid crystals, 4-cyano-4'-n-pentylbiphenyl, on the two polyim ides were measured by the crystal rotation method. The relative surface ato mic concentrations of F/C (%) were measured by Xray photoelectron spectrosc opy. Electric force microscopy was utilized to investigate the surface elec trostatic property of the two thin polyimide alignment layers before and af ter rubbing. All results demonstrate that rubbing causes trifluoromethyl mo ieties to migrate towards the surface, absorb negative charges and orient a long the rubbing direction. Thus, it is proposed that distributions of func tional groups on the surface of the polyimide after rubbing are anisotropic and the van der Waals forces between the polar groups and liquid crystal m olecules play an important role in the uniform orientation of the liquid cr ystal molecules. (C) 2000 Published by Elsevier Science S.A. All rights res erved.