Like-charge attraction at the nanoscale: ground-state correlations and water destructuring

TL;DR

This paper demonstrates that at the nanoscale, like-charge attraction is primarily governed by ground-state correlations and water destructuring, leading to an effective interaction pressure that explains attraction phenomena without multivalent ions.

Contribution

The authors derive a simple, accurate ground-state-based interaction pressure formula that accounts for water destructuring and explains like-charge attraction at the nanoscale.

Findings

Ground-state correlations dominate even at low correlation strength.

Water destructuring reduces dielectric screening, enhancing ionic correlations.

The derived pressure formula matches simulation results and explains attraction phenomena.

Abstract

Like-charge attraction, driven by ionic correlations, challenges our understanding of electrostatics both in soft and hard matter. For two charged planar surfaces confining counterions and water, we prove that even at relatively low correlation strength, the relevant physics is the ground-state one, oblivious of fluctuations. Based on this, we derive a simple and accurate interaction pressure, that fulfills known exact requirements and can be used as an effective potential. We test this equation against implicit-solvent Monte Carlo simulations and against explicit-solvent simulations of cement and several types of clays. We argue that water destructuring under nanometric confinement drastically reduces dielectric screening, enhancing ionic correlations. Our equation of state at reduced permittivity therefore explains the exotic attractive regime reported for these materials, even in absence of multivalent counterions.