Weak surface anchoring of liquid crystals

Current nematic liquid-crystal (LC) displays rely on voltage-induced reorie ntation of the director (the average molecular direction) within the bulk o f the LC layer. In these devices, the surface region of the LC is strongly anchored to the cell walls and does not undergo reorientation at normal ope rating voltages. This situation is not optimal and indeed modelling has sho wn that weak anchoring of the LC can in principle lead to lower operating v oltages and improved steepness in the electro-optic response(1). Achieving weak anchoring in practice has proved difficult. Soft rubbing of a polymer( 2) or photoinduced ordering of a polymer(3) coating the cell walls can lead to weak azimuthal (in-plane) anchoring, but a memory effect is still prese nt which prevents high-speed surface reorientation. Some surface treatments , such as obliquely evaporated silicon oxide, can also induce weak anchorin g, but only for a restricted range of temperatures(4,5). Here we report a d ifferent approach to weak anchoring, which relies on the addition of small percentages of oligomeric molecules to the LC. This approach results in ver y small zenithal tout of substrate plane) and azimuthal tin plane) anchorin g energies, When applied to nematic displays, such treatments lead to a hal ving of the operating voltage.