A novel method for determining the anchoring energy function at a nematic liquid crystal-wall interface from director distortions at high fields

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Abstract
We show that the anchoring energy function, i.e., the anisotropic part of the interfacial free energy, at a nematic liquid crystal‐wall interface can be determined uniquely without a numerical fitting procedure, when the integrated birefringence of a liquid crystal cell with a thickness much larger than the extrapolation length is measured as a function of an electric or magnetic field well above the Freedericksz threshold. The precision of the present method is closely argued, showing that the resulting anchoring energy function is reasonably insensitive to the uncertainties in the material parameters and in the cell thickness. As an example, the anchoring energy function at the interface between 5CB(pentylcyanobiphenyl) and an obliquely evaporated SiO was determined for the first time, by measuring the birefringence and the capacitance of a 56‐μm‐thick cell up to 150 V rms at 0.23 °C below the clearing temperature. A saturation of the field‐induced distortion was clearly observed at about 100 V rms. The anchoring energy function was found to be well fitted by a function of the form (1)/(2) Ea sin2 θ+ (1)/(4) E1 sin4 θ, where θ is the angle between the boundary director and the substrate, with Ea ∼4.0×10−5 J/m2 and E1∼−1.8×10−5 J/m2.