Fedorenko D. Anchoring of Nematic Liquid Crystal on the Polymer Surface due to Light-Induced Adsorption and Desorption of Dye Molecules.

In this work the light-induced anchoring of liquid crystal (LC) doped with azo-dye was studied. There anchoring appearance and evolution at the aligning tested surface were investigated. The original model of light-induced anchoring was suggested and experimentally examined. The light-induced anchoring appears at the interface of the LC and aligning polymer layer due to competition of three processes: light-induced adsorption and desorption of dye molecules and light-induced bulk torque. This competition makes very complicated the investigation and understanding of the light-induced anchoring evolution. The separation of the processes which govern the effect of light-induced alignment of LC doped with azo-dye allowed to simplify the investigations and follow the evolution of the light-induced anchoring on the non-photosensitive polymer during irradiation. Third, we followed the dynamic of the light-induced anchoring evolution while irradiating the sample in nematic phase. It was established that the combined action of the light-induced adsorption/desorption and the light-induced bulk torque results in a gliding of the easy orientation axis while the light irradiation. The theoretical model was suggested for explanation the experimental data in terms of the light-induced changes of the adsorbed dye molecules angular distribution due to their exchange with the dye molecules from the liquid crystal bulk. There were made the numerical calculation of the dependencies of director reorientation angle and easy axis position on the irradiation time. Calculated dependencies closely fit the experimental data.