Generation of high pretilt angle and surface anchoring strength in nematic liquid crystal on a rubbed polymer surface

The generation of high pretilt angles in nematic liquid crystal (LC), 4-n-pentyl-4-cyanobiphenyl (5CB), on the rubbed surface of polyimide (PI) containing trifluoromethyl moieties, was investigated. High pretilt angles of 5CB are strongly related to the low surface energy caused more by the existence of trifluoromethyl moieties at low rubbing strength (RS). It is considered that the high pretilt angles of 5CB are most likely due to the van der Waals (VDW) dispersion interactions between the LC molecules and polymer surface having low surface energy. The medium and low pretilt angles at high RS may be caused by the combination of the VDW polymer surface with that of the dispersion and the steric interactions between the LC molecules and the asymmetric triangular structure formed by unidirectional rubbing. Finally, it was found that the polar anchoring strength A of 5CB strongly depended on the surface ordering of the rubbed PI surface containing trifluoromethyl moieties; with A decreasing proportionately with increasing RS.