Interfacial solvation explains attraction between like-charged objects in aqueous solution

TL;DR

This paper proposes that interfacial water behavior explains the long-standing puzzle of like-charged attraction in aqueous solutions, challenging traditional electrostatic models.

Contribution

It introduces a novel mechanism based on interfacial solvation to explain like-charged attraction in dilute aqueous solutions, bridging experimental observations and theoretical understanding.

Findings

Interfacial water behavior causes attraction between like-charged objects.

The mechanism applies broadly across various experimental conditions.

It challenges traditional electrostatic models of colloidal interactions.

Abstract

Over the past few decades the experimental literature has consistently reported observations of attraction between like-charged colloidal particles and macromolecules in solution. Examples include nucleic acids and colloidal particles in bulk solution and under confinement, and biological liquid-liquid phase separation. This observation is at odds with the intuitive expectation of an interparticle repulsion that decays monotonically with distance. Although attraction between like-charged particles can be theoretically rationalised in the strong-coupling regime, for example, in the presence of multivalent counterions, recurring accounts of long-range attraction in aqueous solution containing monovalent ions at low ionic strength have posed an open conundrum. Here we show that the behaviour of molecular water at an interface - traditionally disregarded in the continuum electrostatics picture, provides a mechanism to explain attraction between like-charged objects in a broad spectrum of experiments. This basic principle will have important ramifications in the ongoing quest to better understand intermolecular interactions in solution.