INFLUENCE OF SPATIAL INHOMOGENEITIES ON THE FREEDERICKSZ THRESHOLD

By analyzing the Freedericksz transition induced by an external magnet ic field on a nematic liquid crystal, we determine the elastic contrib ution to the anisotropic part of the anchoring energy. Our result is i n good agreement with the one obtained by other groups for the same pr oblem. In the simple case in which the elastic constants change in a s urface layer whose thickness is very small with respect to the thickne ss of the sample, our analysis shows that the extrapolation length of elastic origin is of the order of the thickness of the surface layer. The influence of the spatial variation of the diamagnetic anisotropy i s also analyzed. It is shown that the contribution to the surface ener gy, arising from this spatial variation, is negligible.