Photoalignment in the isotropic phase of liquid crystal on chalcogenide glass film

Abstract

We discovered the phenomenon of liquid crystal (LC) alignment on a photosensitive chalcogenide glass film As20Se80 after irradiation of the LC in the isotropic phase with polarised light. The photoalignment was observed after cooling of the LC to the nematic phase. Quality of the photoalignment depended on an initial phase state of the LC. If the photoalignment was uniform at the irradiation of the isotropic phase of the LC that initially was pre-aligned in the nematic phase, the irradiation of the cell being filled in the isotropic phase resulted in inhomogeneous photoalignment. The orientation of the LC strongly depended on the geometry of the irradiation the LC in the cell. In the case of the direct irradiation of the chalcogenide surface, the photoorientation of the LC was stable. On the contrary, the irradiation of the chalcogenide surface through the LC layer led to the temporal photoalignment that diminished within few days. The results are explained in the frame of the model that suggests two mechanisms of photoalignment. The first one is related to a light-induced anisotropy on chalcogenide layer and the second one involves a LC in the process. We assume that an anisotropic light-induced desorption of LC molecules from the chalcogenide layer is the origin of last kind of photoalignment. The asymmetry of the photoalignment properties at the irradiation from the different sides of the chalcogenide surface is explained by producing different surface structures at the irradiation from the different sides.