Dressed Counterions: Strong Electrostatic Coupling in the Presence of Salt

TL;DR

This paper develops a combined weak-strong electrostatic coupling theory to describe asymmetric electrolyte solutions with salt and polyvalent counterions, validated by Monte-Carlo simulations for charged surfaces.

Contribution

It introduces a novel asymmetric field-theoretical approach integrating weak and strong coupling methods for electrolytes with salt and polyvalent ions.

Findings

Good agreement with Monte-Carlo simulations at high electrostatic coupling.

Identification of two limiting laws that fit all simulation data.

Enhanced understanding of correlation attraction mediated by polyvalent counterions.

Abstract

We reformulate the theory of strong electrostatic coupling in order to describe an asymmetric electrolyte solution of monovalent salt ions and polyvalent counterions using field-theoretical techniques and Monte-Carlo simulations. The theory is based on an asymmetric treatment of the different components of the electrolyte solution. The weak coupling Debye-Huckel approach is used in order to describe the monovalent salt ions while a strong coupling approach is used to tackle the polyvalent counterions. This combined weak-strong coupling approach effectively leads to dressed interactions between polyvalent counterions and thus directly affects the correlation attraction mediated by polyvalent counterions between like-charged objects. The general theory is specifically applied to a system composed of two uniformly charged plane-parallel surfaces in the presence of salt and polyvalent counterions. In the strong coupling limit for polyvalent counterions the comparison with Monte-Carlo simulations shows good agreement for large enough values of the electrostatic coupling parameter. We delineate two limiting laws that in fact encompass all the Monte-Carlo data.