Phase equilibria in a model of low-salt suspensions of charged colloids

We calculate phase diagrams of low-salt suspensions of charged colloidal particles using a recently proposed effective one-component Hamiltonian for the colloids (van Roil R, Dijkstra M and Hansen J-P 1999 Phys. Rev. E 59 2010). This Hamiltonian consists of the purely repulsive pairwise Derjaguin, Landau, Verwey, and Overbeek (DLVO) potential and density-dependent volume terms. The latter play a crucial role in driving phase transitions at salt concentrations of the order of 10 mu M or lower. We find phase diagrams that exhibit gas-liquid coexistence with upper and lower critical points, and, for sufficiently large surface charge densities, upper and lower gas-liquid-solid triple points. A connection between the Debye-Huckel theory for simple electrolytes and the DLVO theory for colloidal suspensions is made.