Phase diagram of mixtures of colloids and polymers in the thermal crossover from good to $\theta$ solvent

TL;DR

This study maps the phase diagram of colloid-polymer mixtures across the thermal crossover from theta to good solvent conditions, highlighting solvent quality effects on phase behavior using generalized free-volume theory.

Contribution

It applies and extends the generalized free-volume theory to analyze phase diagrams in the thermal crossover region, providing new insights into solvent quality impacts.

Findings

Phase diagram is insensitive to solvent quality near the theta point.

Solvent quality significantly shifts critical points and binodals near the good-solvent regime.

GFVT accurately predicts phase behavior for $q = R_g/R_c \, \lesssim 1$.

Abstract

We determine the phase diagram of mixtures of spherical colloids and neutral nonadsorbing polymers in the thermal crossover region between the $\theta$ point and the good-solvent regime. We use the generalized free-volume theory (GFVT), which turns out to be quite accurate as long as $q = R_g/R_c\lesssim 1$ ($R_g$ is the radius of gyration of the polymer and $R_c$ is the colloid radius). Close to the $\theta$ point the phase diagram is not very sensitive to solvent quality, while, close to the good-solvent region, changes of the solvent quality modify significantly the position of the critical point and of the binodals. We also analyze the phase behavior of aqueous solutions of charged colloids and polymers, using the extension of GFVT proposed by Fortini et al., J. Chem. Phys. 128, 024904 (2008).