THE ISOTROPIC-NEMATIC PHASE-TRANSITION IN A FLUID OF SQUARE-WELL SPHEROCYLINDERS

The isotropic-nematic phase transition in a fluid of hard spherocylind ers with a spherocylindrical square-well attraction is examined using Monte Carlo simulations and two theoretical approaches. The first theo ry is a first-order perturbation theory which incorporates the Parsons decoupling approximation for the pair distribution function. The seco nd theory is a simple resummation of the virial coefficients in the ne matic phase which maps the thermodynamics of the nematic phase to thos e of the isotropic phase. In general both the theoretical approaches a nd the simulation results show a destabilization of the nematic phase with respect to the isotropic phase as the temperature is decreased. H owever, close comparison between the simulation results and the theori es reveals that the Parsons approach is quantitatively deficient. On t he other hand, the results for the resummation procedure are in good a greement with the simulation results over the full isotropic range and for the isotropic-nematic phase transition. The comparison of the nem atic phase close to the phase transition shows reasonable agreement be tween theory and simulation, however, the theoretical results become m uch poorer deep in the nematic phase. The reason for this is attribute d to the crude manner in which the orientational dependence is include d into the attractive contribution to the free energy. (C) 1998 Americ an Institute of Physics.