Validity of the Landau Approximation in the Nematic Phase

Abstract

The Landau approximation is known to give a good description of the pretransitional phenomena in the isotropic phase of nematic liquid crystals. We prove that, in the nematic phase too, just below the nematic-isotropic transition, the variations with temperature of the order parameter Q are well described by the theory based on the Landau expansion of the free energy F. The coefficients of the expansion of F are determined and the variations of F with Q are given for two nematic liquid crystals. The calculated values of Tc - T∗ and of the latent heats are in good agreement with the values obtained by independent way.