ON THE VALIDITY OF THE ELASTIC MODEL FOR THE NEMATIC SURFACE ANCHORING ENERGY

The intrinsic uniform and non-uniform contributions to the anisotropic part of the surface energy are considered. Our analysis shows that th e uniform part can be separated into an intrinsic and an extrinsic ter m. The first one is due to the nematic-nematic interaction only, where as the second one is due to the nematic-substrate interaction. They ar e found to be of the same order of magnitude (approximate to 1 erg cm( 2)). The non-uniform part takes its origin from the spatial variation of the elastic constants. By means of a semi-microscopic model it is s hown that, in the framework of perfect nematic order, the extrapolatio n length of the elastic origin is microscopic. On the contrary, if the spatial variation of the scalar order parameter is taken into account , simple calculations indicate that the extrapolation length is of the order of the coherence length in the nematic phase.