ANISOTROPIC ALIGNMENT OF A NEMATIC LIQUID-CRYSTAL CONTROLLED BY A POLARIZATION-SENSITIVE LANGMUIR-BLODGETT COMMAND LAYER

We investigate the homeotropic double-line arrow pointing left and right planar switching in the alignment of a nematic liquid crystal (LC) controlled by Langmuir-Blodgett command layers of polymer containing photochromic azobenzene molecules in the side chain. Waveguide spectroscopy is used to probe the changes in the optical properties of the LC induced by the cis <-->trans photoisomerization of the azobenzene units. This optical method provides a high sensitivity for studying the orientation of the LC both within and perpendicular to the plane of waveguide cell. The study of the dynamics of the switching induced by polarized uv light shows that initially the LC molecules follow the movement of the azobenzene units but that eventually they align with the dipping direction. An explanation for this effect based on the movement of the azobenzene units themselves is proposed.