Optical measurement of azimuthal anchoring strength in nematic liquid crystals

We have observed the azimuthal switching at the interface of nematic liquid crystals (LCs) and the aligning substrate, induced by the planar electric field of a fine comb electrode. Optical transmittance as a function of applied voltage was modeled by both the elastic theory with rigid anchoring and the Landau-de Gennes theory with the interfacial energy expression 1/2Wtr[(Q two down arrows -Q two down arrows (0))(2)], where Q two down arrows is the liquid crystal order parameter and Q two down arrows (0) is the surface order parameter induced by the aligning substrate. Optical data on the in-plane switching LC cells were found to differ qualitatively with the predictions of the rigid anchoring model but to agree well with those of the Landau-de Gennes theory. We obtain not only the strength W of the azimuthal anchoring, but also find the surface order parameter S(surface) to be 20-30 % less than that of the bulk. The optically measured azimuthal anchoring strength is in good agreement with the literature values determined through other means.