ELASTIC-CONSTANTS IN A PSEUDOMOLECULAR APPROACH FOR A MIXED MAIER-SAUPE AND NEHRING-SAUPE INTERACTION LAW

A pseudomolecular approach is employed to calculate the elastic consta nts of a nematic liquid crystal by assuming an interaction volume of e llipsoidal shape. We consider a special kind of mixed Maier-Saupe and Nehring-Saupe interaction law characterized by a mixing factor epsilon . To epsilon=0 corresponds the Maier-Saupe law, whereas to the case ep silon=1 corresponds the induced dipole-induced dipole interaction law. The dependence of the elastic constants on the eccentricity of the mo lecular volume shape and on the mixing factor is investigated by means of a numerical analysis. We show that, for particular values of the e ccentricity, the K-11 (splay) and K-33 (bend) elastic constants become negative for some values of the mixing factor. Moreover, the nonmonot onic behavior of the splay-bend elastic constant with respect to the m ixing factor, already reported in a spherical approximation for the in teraction volume, is also observed. This result reinforces the indicat ion that the subsurface deformations, if any, are not only due to the splay-bend term.