Attraction Between Like-Charge Surfaces in Polar Mixtures

TL;DR

This paper investigates how two like-charged surfaces in aqueous mixtures experience attraction due to phase condensation, with analytical and numerical results showing long-range attraction at specific distances.

Contribution

It provides a detailed analysis of the force between charged surfaces in mixtures, revealing phase condensation effects and osmotic pressure behavior at nanometer scales.

Findings

Water-rich phase condenses at nanometer distances

Osmotic pressure becomes negative, causing attraction

Analytical and numerical results for condensation distances

Abstract

We examine the force between two charged surfaces immersed in aqueous mixtures having a coexistence curve. For a homogeneous water-poor phase, as the distance between the surfaces is decreased, a water-rich phase condenses at a distance $D_t$ in the range 1-100nm. At this distance the osmotic pressure can become negative leading to a long-range attraction between the surfaces. The osmotic pressure vanishes at a distance $D_e<D_t$, representing a very deep metastable or globally stable energetic state. We give analytical and numerical results for $D_t$ and $D_e$ on the Poisson-Boltzmann level.