Macroion Attraction Due to Electrostatic Correlation between Screening Counterions. 1. Mobile Surface-Adsorbed Ions and Diffuse Ion Cloud

Abstract

Highly charged macroion surfaces in solutions of multivalent electrolytes attract each other electrostatically through correlations in their counterion environment. We show that significant correlation occurs when the counterion distribution has a pseudo-two-dimensional character. This allows us to treat the electrostatic correlation attraction semianalytically by reducing the problem to interaction between layers of adsorbed but mobile counterions neutralizing surfaces of similar charge density. Both when the counterion distribution is in the two-dimensional limit, and when it has a more realistic three-dimensional character, Coulomb repulsion between counterions produces an alternation of positive and negative charges at the surface. Two such apposing patterns adjust complementarily to each other, resulting in electrostatic attraction of the surfaces. The magnitude of this attraction depends solely on the surface charge density and the solution dielectric constant, while its range is defined by the size of the planar correlation hole around each ion. The attraction is stable with respect to the disruptive influence of planar thermal motion of the ions. The theory enables construction of a universal function which, after being scaled with the appropriate parameters of the system, yields the attractive electrostatic correlation pressure.