Orientations of phenyl sidegroups and liquid crystal molecules on a rubbed polystyrene surface

Surface-specific sum-frequency vibrational spectroscopy and second-harmonic generation have been used to study the structure of a rubbed polystyrene (PS) surface and the orientation of 4^′-n-pentyl-4-cyanobiphenyl (5CB) liquid crystal molecules on it. The results show that the phenyl sidegroups are well aligned by rubbing in the direction perpendicular to rubbing but tilt from the surface normal with a broad distribution. Although the PS surface is nonpolar, the 5CB molecules appear to adsorb on PS preferentially with the terminal cyano group facing the PS surface.