SURFACE ORIENTATION OF POLYIMIDE ALIGNMENT LAYER STUDIED BY OPTICAL 2ND-HARMONIC GENERATION

We have determined the orientational distribution function (ODF) of th e side chains of polyimide films for liquid crystal alignment. To dete rmine ODF, optical second-harmonic generation was measured as a functi on of sample rotation angle. Using nonlinear susceptibility components obtained by a fitting procedure, ODF was obtained by means of informa tion entropy. The symmetry of the polymer side chains changes from C-x v to C-s by rubbing treatment. Asymmetry of the polar angle along the rubbing direction is induced, though the change is very small.