Computer simulation studies of anisotropic systems XXVII: phase diagram for a nematic binary mixture

摘要

Continuing previous work, we present here the phase diagram of a binary mixture consisting of a nematogenic solvent and a solute of spherical particles obtained using the Monte Carlo computer simulations. In this mixture the rod-like particles interact via a Lebwhol-Lasher potential while the spherical particles are represented by vacancies; all particles are located on the sties of a simple cubic lattice. There are two types of motion allowed, namely rotation of the rod-like particles and exchange of lattice positions between a pair of solute and solvent particles. Various exchange procedures ensuring preservation of microscopic reversibility conditions between unlike particles have been investigated and the one leading to computationally fastest convergence of various averages identified. Simulation results suggest a broader region of uniform nematic phase which transforms directly into the isotropic phase at a higher temperature in contrast to the molecular field prediction of a narrow single nematic phase surrounded by the nematic-isotropic coexistence region. Moreover there was no evidence of any biphasic region just below the clearing point although demanded by the first order nature of the phase transition. For mixtures with a solute mole fraction higher than 40 percent, only one weak transition, which apparently is that of a biphasic into the isotropic phase, was observed.