Role of Surface Hydrophobicity in Pretilt Angle Control of Polymer-Stabilized Liquid Crystal Alignment Systems

A certain amount of photocurable monomers biphenyl diacrylate and lauryl acrylate was added to liquid crystal (LC) molecules. The LC alignment was stabilized with a certain pretilt angle after a fixed amount of UV exposure under an applied voltage to the LC cell. The pretilt angle of the LC was successfully adjusted over the whole range from 0.8 degrees to 90 degrees continuously by simply increasing the monomer concentration in the LCs. Polymer bumps formed with a rather uniform size around 250 nm in diameter, and chain-like clusters were found on the polymer-coated substrate. The advancing contact angle of water was applied as an index of the surface hydrophobicity. The pretilt angle of the LC monotonically increases along with an increase in the advancing contact angle of water on the polymer-coated substrate. The surface hydrophobicity of the substrate plays an essential role in governing the pretilt angle in the polymer-stabilized LC alignment system.