Surface Transition in a Nematic Layer with Reverse Pretilt

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Abstract
Recently, a surface induced transition from homeotropic to planar alignment in a nematic layer and the corresponding optical response has been reported/K. Flatischler, L. Komitov, S. T. Lagerwall, B. Stebler, and A. Strigazzi, Mol. Cryst. Liq. Cryst., 198, 119 (1991)/. In the case of surface conditions with reverse pretilt a similar transition from quasi-homeotropic bent alignment to quasi-planar splayed state can be obtained. As known, these two states are topologically incompatible, and therefore the transition is accompanied by nucleation of π-disclination lines, and even is reversible, it exhibits a big hysteresis. Moreover, it can be driven not only by temperature but also by an applied electric field, using a nematic with negative dielectric anisotropy. A simple theoretical description of such an alignment transition is presented.