Perturbation method for incorporating the concentration dependence of the Flory–Huggins parameter into the theory of steric stabilization

Abstract

Theories for the mixing contribution to steric stabilization assume that the Flory–Huggins interaction parameter (χ) is constant whereas experiments demonstrate that χ is usually concentration dependent. A perturbation method is elaborated that allows this concentration dependence to be incorporated into the theory for steric stabilization. It is shown that the first order perturbation term, if compared with the leading term, is of order ν, where ν is the mean segment volume fraction in the steric barrier. Consequently, the concentration dependence may contribute significantly to the repulsion, especially for low molecular weight polymers and high compressions. The complete mixing term is evaluated for the simple model of a constant segment density. The predictions of the theory are compared with the experimental disjoining pressures recently reported by Homola and Robertson. The correlation between the critical flocculation point and the theta-point is not significantly affected by the concentration dependence of χ.