The isotropic-nematic transition of dipolar spherocylinders: combining thermodynamic perturbation with Monte Carlo simulation

Abstract

We attempt to predict the phase behaviour of elongated molecules possessing longitudinal point dipoles by treating the dipolar interaction as a perturbation on a reference system consisting of hard spherocylinders. Thermal averages of up to the fourth power of the total dipolar interaction are evaluated by Monte Carlo simulation in the NVT ensemble of the nonpolar spherocylinders over a range of densities spanning the isotropic-nematic transition density. From the evaluation of the first two terms in the high-temperature perturbation expansion of the free energy we find that the nematic phase is destabilized relative to the isotropic phase (when compared with the non-polar system) as one switches on a weak central dipolar interaction. In contrast, off-centre dipoles appear to have a stabilizing effect on the nematic phase for weak dipoles, but as the dipole strength increases the nematic is seen to be destabilized with respect to the isotropic phase.