Charged colloids in an aqueous mixture with a salt

TL;DR

This paper models ion and composition distributions around colloids in aqueous mixtures, revealing phase transitions and altered interactions due to preferential adsorption, electrostatics, and solvation effects.

Contribution

It introduces a comprehensive theoretical framework accounting for multiple interactions and predicts surface phase transitions affecting colloid interactions.

Findings

Precipitation transition induced by hydrophilic ion preference.

Wetting layers significantly amplify colloid interactions.

Transitions extend far from the solvent coexistence curve.

Abstract

We calculate the ion and composition distributions around colloid particles in an aqueous mixture, accounting for preferential adsorption, electrostatic interaction, selective solvation among ions and polar molecules, and composition-dependent ionization. On the colloid surface, we predict a precipitation transition induced by strong preference of hydrophilic ions to water and a prewetting transition between weak and strong adsorption and ionization. These transition lines extend far from the solvent coexistence curve in the plane of the interaction parameter \chi (or the temperature) and the average solvent composition. The colloid interaction is drastically altered by these phase transitions on the surface. In particular, the interaction is much amplified upon bridging of wetting layers formed above the precipitation line. Such wetting layers can either completely or partially cover the colloid surface depending on the average solvent composition.