Electric double layer force between charged surfaces: Effect of solvent polarization

Abstract

In this paper, we develop a theory to delineate the consequences of finite solvent polarization in electric double layer interaction or the osmotic pressure between two similar or oppositely charged surfaces. We use previously published Langevin-Bikerman equations to calculate this electric double layer interaction force or the osmotic pressure between the charged surfaces. The osmotic pressure between oppositely charged surfaces is found to be much larger than that between similarly charged surfaces, and for either case, the influence of solvent polarization ensures a larger pressure than that predicted by the Poisson-Boltzmann (PB) model. We derive distinct scaling relationships to explain the increase of the pressure as a function of the separation between the surfaces, the solvent polarizability, and the number density of water molecules. Most importantly, we demonstrate that our theory can successfully reproduce the experimental results of interaction force between similar and oppositely charged surfaces, by accounting for the large under-prediction made by the corresponding PB model.