LANDAU THEORY OF THE NEMATIC-ISOTROPIC PHASE-TRANSITION

The influence of the surface properties and the sample thickness on the critical temperature of the nematic-isotropic phase transition is theoretically analyzed. By using the Landau expression for the free-energy density it is shown that the sample thickness can strongly influence the phase transition. In particular our analysis demonstrates that it is possible to define a typical length connected with the surface properties of the substrate and with the elastic properties of the nematic material. When this length is much smaller than the sample thickness the ideal situation of homogeneous sample holds. On the other hand if this characteristic surface length is of the order of the sample thickness some peculiar surface length behaviour in the phase transition appears.