Clustering and percolation in dipolar hard-sphere fluids.

Abstract

Clustering and continuum percolation in dipolar fluids are studied through Monte Carlo simulation and connectedness theory with an emphasis on the effect of the dipole-dipole interactions on the size and shape of the clusters and on the threshold percolation density. Two simple models for the dipolar fluid are considered: (i) a system of hard spheres with an embedded point dipole and (ii) a related system of hard spheres in which the dipole-dipole forces are replaced by an angular-averaged dipolar potential. A first-order perturbation theory (for the first model) and the connectedness version of the Percus-Yevick integral equation (for the second one) are used to describe clustering and percolation, and their results are compared with the corresponding Monte Carlo data. Our results show that clusters become larger in size and acquire a stronger mean dipolar moment when the particles' dipolar moments are increased. Far from the percolation transition, the clusters are nonspherical, the eccentricity being favored by the energetics of dipolar orientation. Furthermore, they reveal that larger dipolar strengths imply smaller percolation densities.