Simulation and theory of fluid demixing and interfacial tension of mixtures of colloids and non-ideal polymers

TL;DR

This paper extends the AO model to include polymer non-ideality with a repulsive stepfunction, using simulations and density functional theory to study fluid demixing and interfacial tension in colloid-polymer mixtures.

Contribution

It introduces a modified model accounting for polymer non-ideality and validates theoretical predictions with simulations for demixing behavior and interfacial tension.

Findings

Polymer non-ideality shifts the fluid demixing binodal.

Interfacial tension decreases with increased polymer-polymer repulsion at fixed colloid density.

Interfacial tension increases with polymer reservoir packing fraction at fixed colloid density.

Abstract

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