Mechanisms of liquid crystal alignment on buffed polyimide surfaces

The surfaces of poly(amic acid) and cured polyimide films, subjected to different buffing and cure profiles, have been examined by atomic force microscopy (AFM). The ability of these buffed polymer surfaces to align nematic and chiral smectic C liquid crystals were also investigated. These studies show that the presence of microgrooves on buffed polymer surfaces are not necessary for alignment of liquid crystals. Rather, it is concluded that the liquid crystal alignment is mainly caused by the anisotropic intermolecular interactions between liquid crystal molecules and the polymer chains oriented by buffing. For the alignment of smectics, both the degree of order and mechanical properties of polyimide films are found to be important factors.