# Screening length for finite-size ions in concentrated electrolytes

## TL;DR

This paper investigates how finite ion size influences the screening length in concentrated electrolytes, revealing non-monotonic behavior and charge oscillations beyond classical Debye-Huckel theory.

## Contribution

It introduces a modified Coulomb interaction kernel that accounts for ion size, predicting non-monotonic screening length dependence and charge oscillations at high concentrations.

## Key findings

- Screening length increases with ion concentration in concentrated solutions.
- Charge-charge correlations exhibit damped oscillations at high concentrations.
- Ion size significantly affects electrostatic screening behavior.

## Abstract

The classical Debye-Huckel (DH) theory clearly accounts for the origin of screening in electrolyte solutions and works rather well for dilute electrolyte solutions. While the Debye screening length decreases with the ion concentration and is independent of ion size, recent surface-force measurements imply that for concentrated solutions, the screening length exhibits an opposite trend; it increases with ion concentration and depends on the ionic size. The screening length is usually defined by the response of the electrolyte solution to a test charge, but can equivalently be derived from the charge-charge correlation function. By going beyond DH theory, we predict the effects of ion size on the charge-charge correlation function. A simple modification of the Coulomb interaction kernel to account for the excluded volume of neighboring ions yields a non-monotonic dependence of the screening length (correlation length) on the ionic concentration, as well as damped charge oscillations for high concentrations.