Correlations between surface and bulk liquid crystal alignment observed with optical second-harmonic generation

We report a direct experimental observation of surface-induced liquid crystal (LC) monolayer orientation and its relation to the LC bulk alignment. Using optical second-harmonic generation from these LC monolayers, adsorbed on rubbed polymer surfaces, we determined both the polar and azimuthal orientation of the LC molecules. A close correlation between the rubbing-induced azimuthal orientational distribution of the LC monolayers and the resulting LC bulk pretilt angle has been observed. A simple model based on epitaxial growth of the bulk LC on top of the first LC monolayer is proposed to explain this correlation.