Analytic liquid state theory of the polymer-mediated depletion interaction between colloids beyond preaveraging approximation.

Abstract

We develop a version of the polymer reference interaction site model of the polymer-mediated depletion interaction not relying on the conventional preaveraging of the polymer correlation functions (so-called "preaveraging of the polymer end effects"). The developed approach makes it possible to properly take into account the entropic interactions between the polymers and colloid surfaces, imposed by the polymer end effects. These entropic interactions are shown to give rise to an additional long-ranged contribution to the depletion potential that is comparable to its main osmotic part. The presence of the described entropic interactions essentially changes, in particular, the dependence of the second virial coefficient on the colloid radius. Based on the detailed comparison with the simulations in the work of Doxastakis et al. [J. Chem. Phys. 123, 034901 (2005)], we suggest that the described entropic effect gives an explanation for the fact that the range of the depletion potential obtained in these simulations is of the order of the polymer gyration radius even at relatively large polymer densities.