Perspective: Coulomb fluids -- weak coupling, strong coupling, in between and beyond

TL;DR

This paper reviews the current understanding of Coulomb fluids, focusing on weak and strong coupling regimes, and extends the formalism to complex systems like asymmetric ionic mixtures and polarizable ions, providing new insights.

Contribution

It introduces a systematic derivation of weak and strong coupling limits for various Coulomb fluid systems, including complex cases with additional length scales and ion properties.

Findings

Formalism for weak and strong coupling limits in Coulomb fluids

Extension to asymmetric ionic mixtures and polarizable ions

New insights into properties of complex Coulomb systems

Abstract

We present a personal view on the current state of statistical mechanics of Coulomb fluids with special emphasis on the interactions between macromolecular surfaces, concentrating on the weak and the strong coupling limits. Both are introduced for a (primitive) counterion-only system in the presence of macroscopic, uniformly charged boundaries, where they can be derived systematically. Later we show how this formalism can be generalized to the cases with additional characteristic length scales that introduce new coupling parameters into the problem. These cases most notably include asymmetric ionic mixtures with mono- and multivalent ions that couple differently to charged surfaces, ions with internal charge (multipolar) structure and finite static polarizability, where weak and strong coupling limits can be constructed by analogy with the counterion-only case and lead to important new insights into their properties that can not be derived by any other means.