The calculation of depletion layer thickness as a function of bulk polymer concentration

Abstract

An analytical expression is derived for the depletion layer thickness, at a hard, flat surface in contact with a non-adsorbing polymer solution, as a function of polymer molar mass, concentration and solvency parameter ( X). The approach used is based on the idea that the osmotic pressure of the bulk polymer solution leads to (elastic) compression of any chains near the interface. This model leads to a continuous variation of the depletion layer thickness over the whole polymer concentration range, and not just in the semi-dilute region and beyond as in the de Gennes scaling model. Comparisons of the theory presented here are made with the de Gennes model and also with the Scheutjens—Fleer self-consistent, mean-field lattice model for depletion.