Potential distribution theorem for the polymer-induced depletion between colloidal particles.

The authors investigated the polymer-mediated colloidal interactions in a good solvent wherein the particle size varies from that much smaller than the polymer radius of gyration up to macroscopic and the polymer concentration varies from that corresponding to a dilute solution to that close to a melt. At conditions directly accessible to molecular simulations, the theoretical predictions agree favorably with the simulation results for the distributions of polymer segments and for the polymer-mediated colloidal interactions. The theoretical methods were then exploited to examine the polymer structure and colloidal interactions when the particle/polymer size ratio changes from the "protein" limit to the "colloid" limit at different regimes of the polymer concentration (i.e., dilute, semidilute, and concentrated). The authors found that the surface curvature plays a significant role on the distribution of polymer segments near the particle surface at low polymer concentration, but this effect diminishes as the polymer concentration increases. The Derjaguin approximation works reasonably well at high polymer concentration even in the protein limit, but it may fail qualitatively at low polymer concentration where the polymer-induced colloidal force becomes long range.