Simulation and theory of fluid demixing and interfacial tension of mixtures of colloids and nonideal polymers

An extension of the Asakura-Oosawa-Vrij model of hard sphere colloids and nonadsorbing polymers is studied with grand canonical Monte Carlo simulations and density functional theory. Polymer nonideality is taken into account through a repulsive step-function pair potential between polymers. Simulation results validate previous theoretical findings for the shift of the bulk fluid demixing binodal upon increasing strength of polymer-polymer repulsion, indicating suppression of phase separation. For increasing strength of the polymer-polymer repulsion, simulation and theory consistently predict the interfacial tension of the free interface between the colloidal liquid and the colloidal gas phase to decrease significantly for fixed colloid density difference in the coexisting phases, and to increase for fixed polymer reservoir packing fraction.