Cálculo das constantes elásticas de um cristal líquido nemático: interação quadrupolar

Abstract

The elastic constants of an Nematic Liquid Crystals (NLC) system are evaluated by assuming that the quadrupolar interaction is the only one responsible for the NLC phase. We consider a more realistic and general situation, by assuming an interaction volume of ellipsoidal shape and a screened intermolecular (quadrupolar) potential. The introduction of an anisotropic interaction volume permits a detailed investigation of the behavior of the elastic constants as a function of this anisotropy, represented by the eccentricity e of the ellipsoidal volume. The bulk elastic constants are negative for e = 0 (spherical approximation) and monotonically increasing function of e, as e → 1, remaining negative in the entire range of the values of the eccentricity. On the contrary, the surface-like constants K13 and K24 are positive at e = 0 and become negative for e > 0:9. Therefore, the pseudo-molecular model shows that the quadrupolar interaction energy alone cannot give rise to an NLC phase.