Depletion interaction between two colloidal particles in a nonadsorbing polymer solution.

The depletion effect between two spherical colloidal particles in nonadsorbing polymer solutions is investigated using the self-consistent field theory. The density distributions of polymer segments, the depleted amount and depletion potential are calculated numerically in bispherical coordinates. The effects of chain length, bulk concentration, and solvency are also investigated. In the dilute regime the depleted amount and the depletion potential decrease as the two spherical particles approach to each other. The depth of interaction increases and the width of interaction varies slightly with increasing bulk concentrations. In the semidilute regime, with increasing bulk concentrations the width of interaction decreases and the depth of interaction increases. No distinct repulsive potential is observed in semidilute regime. However, at high concentration the depleted amount exhibits a barrier. The width and the depth of depletion potential increase with increasing the chain length and the solvency. The contact potential is proportional to the polymer concentration and almost independent on the solvency. In addition, the effect of depletion interaction on colloidal stability is analyzed.