Weak surface anchoring of liquid crystals

Abstract

Current nematic liquid-crystal (LC) displays rely on voltage-induced reorientation of the director (the average molecular direction) within the bulk of 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 operating voltages. This situation is not optimal and indeed modelling has shown that weak anchoring of the LC can in principle lead to lower operating voltages and improved steepness in the electro-optic response¹. Achieving weak anchoring in practice has proved difficult. Soft rubbing of a polymer² or photoinduced ordering of a polymer³ coating the cell walls can lead to weak azimuthal (in-plane) anchoring, but a memory effect is still present which prevents high-speed surface reorientation. Some surface treatments, such as obliquely evaporated silicon oxide, can also induce weak anchoring, but only for a restricted range of temperatures⁴,⁵. Here we report a different approach to weak anchoring, which relies on the addition of small percentages of oligomeric molecules to the LC. This approach results in very small zenithal (out ofsubstrate plane) and azimuthal (in plane) anchoring energies. When applied to nematic displays, such treatments lead to a halving of the operating voltage.