Anchoring strength and high pretilt angle in NLC on rubbed organic solvent soluble polyimide surfaces with trifluoromethyl moieties

The polar anchoring energy, the surface order parameter, and the pretilt angles in the nematic liquid crystals (NLC) 4-n-pentyl-4'-cyanobiphenyl (5CB) have been successfully investigated on rubbed soluble polyimide (PI) surfaces with a helical backbone structure and trifluoromethyl moieties. The observed pretilt angle of 5CB is about 15° in the wide rubbing region of rubbed soluble PI surfaces with trifluoromethyl moieties attached to the lateral benzene rings. It is thought that the microscopic surface structure of the polymer contributes to the pretilt angle generation at the surface. Also, we have found that the polar anchoring energy of 5CB is dependent on the molecular structure of the rubbed PI surfaces. The polar anchoring energy of 5CB on the rubbed soluble PI surfaces with trifluoromethyl moieties attached to the lateral benzene rings is smaller than that of the rubbed soluble PI surfaces with trifluoromethyl moieties attached to the polymer backbone. Consequently, the polar anchoring energy of 5CB strongly depends on the surface ordering of the rubbed soluble PI surfaces.