Anchoring transition induced by trans-cis isomerization in photosensitive substrate

A molecular model describing the effective anchoring energy of a liquid crystal (LC) system, composed of 4-n-pentyl-4^{'}-cyanobiphenyl (5CB) molecules deposited on a photosensitive azobenzene layer consisting of 6Az10PVA molecules, is proposed. This model takes into account the interaction between the surface polarization in the LC phase and the surface electric field, arising from the surface charge density. Within the framework of this molecular model, the mechanism responsible for the anchoring transition in the LC phase from homeotropic to planar alignment and vice versa, caused by trans-cis and cis-trans conformational changes in the monolayer 6Az10PVA after laser radiation, is described. It is shown that using experimental data for the voltage across the 6Az10PVA+5CB film, obtained by the surface potential technique, the charge separation during the conformational changing, caused by the laser irradiation, may lead to an anchoring transition induced by trans-cis-trans isomerization in the photosensitive azobenzene monolayer. The calculated values of the isothermal surface pressure diagram π-A showed that the surface area A per LC molecule is noticeably higher for the cis configuration, which reflects a less efficient packaging than in the trans state.