On the basis of a general Rapini and Papoular equation and the unified surface-anchoring energy, surfaceanchoring strength is newly defined theoretically as a function of the azimuthal deviation angle of the surface liquid-crystal directors and the statistical distribution of polyimide chains in a typical twisted nematicliquid-crystal cell. Then these are determined experimentally by the surface second-harmonic generation method, which is nonlinear optics, and the optical phase retardation method. We assume that the anisotropy distribution of polyimide chains induced by the rubbing strength is dominated by a Gaussian distribution around the rubbing direction.
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