Controllable alignment of nematic liquid crystals around microscopic posts: Stabilization of multiple states

Nematic liquid crystal materials are rod-like molecules that align in a locally common direction called the director. This gives rise to anisotropic properties that are used in electro-optical devices such as displays, which usually consist of a sandwich of material between two substrates. The behavior of the director at the substrate surfaces is a critical design consideration, and a wide variety of surface treatments has been reported. Most are dominated by molecular interactions, e.g., high surface energy materials that give homogeneous alignment (the director parallel to substrate). The elastic properties of nematics can also be used to influence alignment by shaping the surface on the micron scale. The potential that this offers to engineer device properties is relatively unexplored; to date, the majority of results reported concentrate on essentially two-dimensional effects. Here we show that the three-dimensional configuration of nematics around microscopic posts results in multiple stable director orientations, and can be used in particular to implement bistable displays with a broad range of control over the optical and switching properties.