Mediation of Long-Range Attraction Selectively between Negatively-Charged Colloids on Surfaces by Solvation

TL;DR

This paper introduces a mean-field model explaining why negatively charged colloids exhibit long-range attraction due to solvation effects, highlighting the asymmetry with positively charged particles and analyzing phase coexistence.

Contribution

It presents a novel analytical model capturing solvation-driven asymmetry in colloidal interactions and applies it to phase behavior of charged disks near interfaces.

Findings

Negatively charged colloids show long-range attraction due to solvation effects.

The model predicts coexistence of ionic and lattice phases based on density and interaction strength.

Asymmetry in colloidal attraction is linked to water-induced short-range repulsion.

Abstract

We propose a mean-field analytical model to account for the observed asymmetry in the ability to form long-range attraction by the negatively charged colloidal particles and not their equivalently charged positive counterpart. We conjecture that this asymmetry is due to solvation effects, and we phenomenologically capture its physics by considering the relative strength of this water-induced short-range repulsion between the different charge species. We then apply our model to the colloidal system of negatively charged disks that are neutralized by a sea of counterions and strongly absorbed to an interface in a compressible binary system. We demonstrate the resulting coexistence between a dilute isotropic ionic phase and a condensed hexagonal lattice phase as a function of density and interaction strength.