Thermodynamic perturbation theory of the phase behaviour of colloid / interacting polymer mixtures

TL;DR

This paper applies thermodynamic perturbation theory to predict phase diagrams of colloid-polymer mixtures, highlighting differences from ideal polymer models and validating results with simulations and explicit two-component models.

Contribution

It introduces a thermodynamic perturbation approach for colloid-polymer mixtures considering polymer interactions, improving phase diagram predictions.

Findings

Phase diagrams differ significantly from ideal polymer models.

Good agreement with explicit two-component simulations.

Polymer interactions influence phase behavior substantially.

Abstract

We use thermodynamic perturbation theory to calculate the free energies and resulting phase diagrams of binary systems of spherical colloidal particles and interacting polymer coils in good solvent within an effective one-component representation of such mixtures, whereby the colloidal particles interact via a polymer-induced depletion potential. MC simulations are used to test the convergence of the high temperature expansion of the free energy. The phase diagrams calculated for several polymer to colloid size ratios differ considerably from the results of similar calculations for mixtures of colloids and ideal (non-interacting) polymers, and are in good overall agreement with the results of an explicit two-component representation of the same system, which includes more than two-body depletion forces.