Optical alignment of liquid crystals

An optical method is described for the preparation of a liquid crystal cell. In one, single exposure step a surface relief grating is generated in a photopolymer layer deposited on a glass substrate. Such substrates then orient liquid crystals in contact with them and homogeneous alignment results. An analysis of the nematic liquid crystal orientation in terms of nematic liquid crystal cell parameters as encountered in applications has been made. Consideration of the different mechanisms proposed to explain the origin of liquid crystal alignment and of the conditions required for the generation of surface relief grating in a photopolymer layer has led to the conclusion that both the photoinduced chromophore theory and the surface oriented polymer chains theory are unable to explain the alignment mechanism. On the other hand, the elastic strain energy theory, which is based on geometrical factors, agrees with the observed spatial molecular orientation of the liquid crystals. (C) 2001 American Institute of Physics.