Mechanism of liquid crystal alignment on submicron patterned surfaces

Abstract

The alignment mechanism of liquid crystals on polymeric surfaces that were patterned using an atomic force microscope (AFM) tip was studied by polarizing optical microscopy. Depending on the thickness of the polymer, polymer chain alignment or grooves appear to be responsible for the liquid crystal alignment. In thick polymer films (above 100 nm) the polymer chains will align in the direction of the scan due to the large lateral force exerted by the tip. In thin polymer films (5–20 nm) the polymer chains are strongly fixed to the surface and will not realign by the tip; instead grooves will be formed. The azimuthal surface anchoring the energy of thick polymer films does not depend on the scan line separation and scan force, is of the same order of magnitude as for conventionally rubbed polyimide surfaces, but increases by the number of scans. AFM patterned pixels do not show a pretilt angle.