title: Attractive ion-ion correlation forces and the dielectric approximation.
abstract: We analyze the classical problem of the interaction between two charged surfaces separated by a solution containing neutralizing counter-ions. The focus is on obtaining a description where the solvent is treated explicitly rather than through a dielectric approximation as is conventionally done. We summarize the results of three papers where we have used a Stockmayer fluid model in Monte Carlo simulations. It is shown that the attractive ion-ion correlation mechanism is also operating when the solvent is described explicitly. There appears an oscillatory component to the force, but when this is accounted for, there is a semi-quantitative agreement between the continuum model and the model with explicit solvent. The properties of the continuum model can be reached in a molecular system by making the solvent molecules much smaller than the ions. It is demonstrated that having an explicit solvent model makes the analysis of force mechanisms more delicate due to the interplay between several different microscopic contributions to the force. Finally, it is argued that the agreement between the forces calculated using the continuum and the explicit solvent models, respectively, has as its basis the circumstance that the force between the surfaces is mainly caused by long-range ion-ion interactions, for which the dielectric approximation is most adequate. This argument applies equally well to an aqueous system as to the Stockmayer fluid.
authors.affiliation: Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB), UMR 6303 CNRS, Univ. Bourgogne Franche-Comté, 9 Av. A. Savary, BP 47870, F-21078 Dijon Cedex, France; Laboratory for Waste Management, Paul Scherrer Institute, Villigen, CH 5232, Switzerland. Electronic address: luis.pegado@u-bourgogne.fr.
authors.forename: Luis
authors.initials: L
authors.lastname: Pegado
authors.affiliation: Division of Theoretical Chemistry, Department of Chemistry, Lund University, PO Box 124, Lund, SE 22100, Sweden.
authors.forename: Bo
authors.initials: B
authors.lastname: Jönsson
authors.affiliation: Division of Physical Chemistry, Department of Chemistry, Lund University, PO Box 124, Lund, SE 22100, Sweden.
authors.forename: Håkan
authors.initials: H
authors.lastname: Wennerström
keywords: Dielectric approximation; Double layer forces; Ion–ion correlations; Molecular solvent; Monte Carlo simulations