Strong coupling electrostatic theory of polymer counterions close to planar charges

TL;DR

This paper develops a strong coupling field theoretic model for polymer counterions near planar charges, analyzing how their shape and size influence electrostatic phenomena like attraction, repulsion, and charge inversion.

Contribution

It introduces a novel strong coupling theory for finite-sized, rod-like polymer counterions, extending beyond point charge models to include shape and volume effects.

Findings

Polymer counterion shape affects density and pressure profiles.

Excluded volume impacts free energy and electrostatic interactions.

Model captures complex phenomena like charge inversion in biological systems.

Abstract

Strong coupling phenomena, such as the like charged macroions attraction, opposite charged macroions repulsion, charge renormalization or charge inversion, are known to be mediated by multivalent counterions. Most theories treat the counterions as point charges, and describe the system by a single coupling parameter that measures the strength of the Coulomb interactions. In many biological systems, the counterions are highly charged and have finite sizes and can be well-described by polyelectrolytes. The shapes and orientations of these polymer counterions play a major role in the thermodynamics of these systems. In this work we apply a field theoretic description in the strong coupling regime to polyelectrolytes. We work out the special cases of rod-like polymer counterions confined by one and two charged walls respectively. The effects of the geometry of the rod-like counterions and the excluded volume of the walls on the density, pressure and the free energy of the rodlike counterions are discussed.