Alignment of nematic liquid crystals on poled photo-polymer films

Abstract

We have studied the alignment of nematic liquid crystals on Electrically Poled Photopolymer (EPP) films. Polarization microscopy studies show different textures in the planar and Twisted Nematic (TN) cells that were made of an EPP substrate and a rubbed-polyimide (PI) substrate. The EPP films exhibit a small pretilt angle of 3 to 5 degrees depending on the cell configuration. In contrast to the small anisotropy of the EPP film compared to Linearly Photo Polymerized (LPP) firms, the azimuthal anchoring strength of the EPP films is larger than that of LPP films and depends on the UV exposure time. 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.