Half-leaky guided wave determination of azimuthal anchoring energy and twist elastic constant of a homogeneously aligned nematic liquid crystal

Optical excitation of half-leaky guided modes has been used to explore the director distortion of a homogeneously aligned nematic liquid crystal (BDH E7) under application of an in-plane electric field. Homogeneous alignment is realized by obliquely evaporated SiOx layers with an in-plane field being applied across a 3 mm gap between gold electrodes. The director is initially aligned approximately parallel to the edges of the electrode gap. By modeling the director profile in the cell to fit the half-leaky guided mode reflectivity data, both with and without applied fields, and then comparing the field induced distortions to continuum theory, we obtain both the twist elastic constant k22 and the surface azimuthal anchoring coefficient, Wa. At 23.7 °C we find that k22=6.5×10−12 N and Wa=2.3×10−6 Jm−2.