  As first explained by the classic Asakura-Oosawa (AO) model, effective
attractive forces between colloidal particles induced by depletion of
nonadsorbing polymers can drive demixing of colloid-polymer mixtures into
colloid-rich and colloid-poor phases, with practical relevance for purification
of water, stability of foods and pharmaceuticals, and macromolecular crowding
in biological cells. By idealizing polymer coils as effective penetrable
spheres, the AO model qualitatively captures the influence of polymer depletion
on thermodynamic phase behavior of colloidal suspensions. In previous work, we
extended the AO model to incorporate aspherical polymer conformations and
showed that fluctuating shapes of random-walk coils can significantly modify
depletion potentials [W. K. Lim and A. R. Denton, Soft Matter 12, 2247 (2016);
J. Chem. Phys. 144, 024904 (2016)]. We further demonstrated that the shapes of
polymers in crowded environments depend sensitively on solvent quality [W. J.
Davis and A. R. Denton, J. Chem. Phys. 149, 124901 (2018)]. Here we apply Monte
Carlo simulation to analyze the influence of solvent quality on depletion
potentials in mixtures of hard sphere colloids and nonadsorbing polymer coils,
modeled as ellipsoids whose principal radii fluctuate according to random-walk
statistics. We consider both self-avoiding and non-self-avoiding random walks,
corresponding to polymers in good and theta solvents, respectively. Our
simulation results demonstrate that depletion of polymers of equal molecular
weight induces much stronger attraction between colloids in good solvents than
in theta solvents and confirm that depletion interactions are significantly
influenced by aspherical polymer conformations.
