Depletion Potentials in Colloid-Polymer Mixtures: Influence of Solvent Quality

The classic Asakura-Oosawa (AO) model first explained how effective attractive forces between colloidal particles induced by depletion of nonadsorbing polymers can drive demixing into colloid-rich and polymer-rich phases, with relevance for water purification, stability of foods and pharmaceuticals, and macromolecular crowding in biological cells. In previous work [1, 2], we extended the AO model to incorporate aspherical polymer conformations and showed that fluctuating shapes of random-walk coils depend sensitively on solvent quality and can significantly modify depletion potentials. Here we use Monte Carlo simulation to analyze how solvent quality affects depletion potentials in mixtures of hard-sphere colloids and nonadsorbing polymers, modeled as ellipsoids whose principal radii fluctuate according to statistics of self-avoiding (good solvent) or non-self-avoiding (theta solvent) random walks. We find that depletion of polymers of equal molecular weight induces much stronger attraction between colloids in good solvents than in theta solvents.

[1] W. J. Davis and A. R. Denton, J. Chem. Phys. 149, 124901 (2018).

[2] W. K. Lim and A. R. Denton, Soft Matter 12, 2247 (2016); J. Chem. Phys. 144, 024904 (2016).