Liquid crystal alignment capabilities on rubbed organic solvent soluble polyimide surfaces with trifluoromethyl moieties

High pretilt angles, polar anchoring energy (out of plane-tilt), and surface ordering in the nematic liquid crystal 4-n-pentyl-4'-cyanobiphenyl (5CB) were investigated on rubbed organic solvent soluble polyimide (PI) surfaces with a helical backbone structure and trifluoromethyl moieties. It was found that the 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 suggested that the microscopic surface structure of the polymer contributes to the LC pretilt angle generation at the surface. Also, the polar anchoring energy of 5CB is dependent on the molecular structure of these unidirectionally rubbed soluble PI surfaces. The polar anchoring strength of 5CB on rubbed soluble PI surfaces is as weak with trifluoromethyl moieties attached to the lateral benzene rings weak as when the trifluoromethyl moieties are attached to the polymer backbone. Finally, the polar anchoring energy of 5CB strongly depends on the surface ordering of rubbed soluble PI surfaces.