We developed a convenient method to prepare command layers for the photocontrol of liquid crystal alignment by surface-selective adsorption of 4-(10-aminodecyloxy)-4'-butylazobenzene (4AzA) on poly(acrylic acid) films. The surface morphology of polymer films was critically affected by the concentration of the azobenzene adsorbate in hexane, and a 2.5×10-5 mol dm-3 solution gave an azobenzene monolayer of a surface density of 2 molecules nm-2 without any modification of the surface morphology of polymer films. The surface density of the azobenzene was controlled by binary systems consisting of 4AzA and n-octadecylamine. Irradiation with an LC cell using a plate of the azobenzene monolayer generated homogeneous alignment with an excellent optical quality and a high resolution power. It was found that a minimum exposure energy of the actinic polarzed ultraviolet light required for the liquid erystal alignment photocontrol was dependent on the surface density of the azobenzene chromophore. No photoresponse was observed for average densities of 4AzA smaller than ca. 0.7 molecules nm-2. The smaller the density of the chromophore on polymer film was, the faster the photoreorientation of the liquid crystal effectively took place.
