ANISOTROPIC ORIENTATIONAL DISTRIBUTIONS OF LIQUID-CRYSTAL MONOLAYERS ON PHOTO-ISOMERIZABLE ALIGNMENT POLYMER-FILMS

We have studied, by measuring surface second-harmonic generation (SHG) , the anisotropy in the orientational distributions of liquid crystal (LC) monolayers on both rubbed polyimide and photo-isomerizable polyim ide films for LC alignment layers. The photo-isomerizable alignment la yer was made by using a main-chain-substituted polyimide with azobenze ne units. Photo-isomerization was achieved by irradiation with linearl y polarized 488 nm light from an Ar-ion laser. The LC molecules, 4-cya no-4'-octylbiphenyl (8CB), were deposited on the alignment layers by u sing the Langmuir-Blodgett (LB) technique. From the surface SHG intens ity profile at 266 nm, it was found that the photo-isomerized layer as well as the rubbed layer can effectively orient the LC molecules towa rd a preferred direction. We also present the nonlinear optical (NLO) susceptibility components of the LC monolayers. Moreover, we compare t he associated surface-order parameters of the LC monolayer on the phot o-isomerizable alignment layer with those of the LC monolayer on the r ubbed polyimide alignment layer.