Alignment of nematic liquid crystals on poled photo-polymer films

We have studied the alignment of nematic liquid crystals on Electrically Po led Photopolymer (EPP) films. Polarization microscopy studies show differen t textures in the planar and Twisted Nematic (TN) cells that were made of a n EPP substrate and a rubbed-polyimide (PI) substrate. The EPP films exhibi t a small pretilt angle of 3 to 5 degrees depending on the cell configurati on. In contrast to the small anisotropy of the EPP film compared to Linearl y Photo Polymerized (LPP) firms, the azimuthal anchoring strength of the EP P films is larger than that of LPP films and depends on the UV exposure tim e. The alignment of EPP films in the TN cells is stable for months whereas the alignment of the LPP films is destroyed within three days.