Gas–liquid phase separation in charged colloidal systems

Abstract

A model system of charged spherical macroions and oppositely charged point counterions with a macroion-charge to counterion-charge ratio Zr=10 was investigated by employing a temperature and density scaling Monte Carlo simulation method. This approach allowed for a determination of the relative free energies among arbitrary number of thermodynamic states over a substantial region of the state space. Here, relative free energies were determined for the macroion volume fraction interval 0.04<φM<0.24 at different values of the electrostatic coupling parameter ΓII≡ZI2LB/RM, where ZI denotes the counterion charge, LB the Bjerrum length, and RM the macroion radius. The binodal curve separating the one-phase system and a gas-liquid two-phase region was determined near the critical point which was determined to φMcr=0.15 and ΓIIcr=2.6.