Detailed investigation on factors governing liquid crystal alignment on rubbed polystyrene films

The molecular orientations and surface morphologies of rubbed films formed from atactic polystyrene (PS) samples with various molecular weights were investigated in detail. Previously unknown surface topography features were newly discovered in rubbed films, depending on molecular weights: submicroscale groove-like meandering structures composed of fine-grooves like pebbles in 10 nm are present, oriented perpendicular to the rubbing direction. The vinyl main chains, however, were preferentially oriented along the rubbing direction and the planes of the phenyl side groups were preferentially oriented perpendicular to the rubbing direction with para-directions that were positioned nearly normal to the film plane. Nematic liquid crystal (LC) molecules were found to always align on the rubbed PS surfaces along the orientation direction of the submicroscale grooves generated by rubbing.