Phase Equilibrium of Colloid Systems with Particle Size Dispersity: A Monte Carlo Study

摘要

We have studied the solid-fluid coexistence for systems of polydisperse soft spheres with near-Gaussian diameter distributions that interact via an inverse power potential, the softness of which is being tuned. The study employs simulation in the isobaric semigrand ensemble. Gibbs-Duhem integration is used to trace the coexistence pressure as a function of the variance of the imposed activity distribution. Both the fluid-solid coexistence densities and volume fractions are monotonically increasing functions of the polydispersity s, which is given in terms of the standard deviation in the particle diameter distribution function. We observe a terminal polydispersity, i.e. a polydispersity above which there can be no fluid-solid coexistence. At the terminus, polydispersity increases from 5.8% to 6.1% to 6.4% and to 6.7% for the solid phase as the softness parameter n, takes on smaller values: from 100 to 50 to 12 and to 10 respectively.