(73f) Ion-Ion Correlation Induced like Charge Attraction and Opposite Charge Repulsion

A statistical mechanics based Gaussian fluctuation theory used previously to model charge inversion (CI) will be presented in the context of Like Charge Attraction between colloidal particles in multivalent salt solutions. At high enough surface charge, our theory predicts that the colloidal surface gets covered by a high-density condensed layer of ions. The attraction between two like charged particles originates in the overlap of these condensed layers on the two surfaces. At very high salt concentrations these condensed layers dissolve into the bulk thereby removing the attractive force component – we believe this to be the reason behind the re-entrant condensation (RC) observed in charged colloidal suspensions. Further, our calculations show that addition of monovalent salts reduces attraction and promotes re-entrant condensation, which agrees with experimental observations. Finally, we relate the phenomenon of opposite charge repulsion with charge inversion where we predict that the former disappears with the disappearance of the latter at higher salt concentrations. Ours is the only theory which can correctly explain both RC and non-monotonic growth of zeta potential after CI in multivalent electrolyte solutions in a single framework.