Tuning the Phase Diagram of Colloid–Polymer Mixtures

Abstract

A theory that predicts the phase behaviour of interacting Yukawa spheres in a solution containing non-adsorbing polymer is presented. It is found that additional Yukawa interactions beyond the hard core affect the location and presence of coexistence regions and phase states. The theoretical phase diagrams are compared with Monte Carlo simulations. The agreement between the two approaches supports the validity of the theoretical approximations made and confirm that, by choosing the parameters of the interaction potentials, tuning of the binodals is possible. The colloidal gas–liquid critical end point (CEP) characterizes the phase diagram topology. It is demonstrated how an additional Yukawa interaction shifts this CEP with respect to the hard sphere case. Provided a certain depletant–to–colloid size ratio for which a stable colloidal gas–liquid phase coexistence takes place for hard spheres, added direct Yukawa interactions turn this into a metastable gas–liquid equilibrium. The opposite case, the induction of a stable gas–liquid coexistence where only fluid–solid was present for hard spheres, is also reported.