Alignment of liquid crystal by patterned isotropic surfaces

Alignment of Liquid Crystals (LCs) has been mostly achieved by microscopically anisotropic surfaces, It is widely believed that anisotropic van der Waals interaction is responsible for the alignment of LCs. We report that isotropic surfaces can align LCs as well when patterned topologically, chemically, and electrically. Stripe-patterned surfaces were produced by photolithography, having periodicity of several microns. The surfaces have either undulation (high and low, topological), alternating polar easy axes (planar and homeotropic, chemical), or alternating conductivity (conducting and non-conducting, electrical). LCs were aligned perpendicularly to the electrical pattern, in contrast to the topological and chemical patterns to which LCs were aligned tangentially. Topologically patterned isotropic surfaces align LCs by the well-known Berreman mechanism. In this report, it is analytically shown that elastic anisotropy and flexoelectricity are responsible for the azimuthal anchoring of LCs on the chemically and electrically patterned surfaces, respectively.