Determination of the surface anchoring potential of a nematic in contact with a substrate

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Abstract
We have developed a method for determining the surface anchoring potential for nematics in contact with a substrate that provides director alignment. Our main result is that the surface torque and hence the anchoring potential may be determined from either dielectric or optical phase response of a nematic undergoing a Freedericksz transition. The method is based on the Frank-Oseen continuum theory, and makes no assumptions about the functional form of the potential. We have measured the surface anchoring potential of two types of substrate in contact with the nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl. The surfaces were ITO-coated float glass, coated either with obliquely evaporated SiO or a buffed polymer film. Comparison of the results obtained from capacitance and optical measurements provides an estimate of the goodness of the method.