Phase behaviour of mixtures of colloidal spheres and excluded-volume polymer chains

We study the phase behaviour of mixtures of colloidal spheres and polymers that have an excluded-volume interaction dispersed in a (background) solvent using the concept of free volume theory. The depletion layer thickness is calculated from the negative adsorption of polymer segments around a sphere. The correlation length and thermodynamic properties of the excluded-volume interacting polymer chains in solution are taken into account by using results from the renormalization group theory. For small polymer-colloid size ratios the difference from an ideal description of the polymers is small, while for larger size ratios the gas-liquid coexistence region shifts in the direction of higher polymer concentrations and at the same time the liquid-crystal coexistence region becomes more extended. Both the gas-liquid region and the gas-liquid-crystal region become less extended, These features are compared to experiment.