Many-body interactions and melting of colloidal crystals

TL;DR

This study investigates how many-body interactions influence the melting of charged colloidal crystals by combining mean-field electrostatics with Brownian dynamics, revealing deviations from pairwise models at low salt concentrations.

Contribution

It introduces a simulation method that fully accounts for many-body effects in colloidal melting, highlighting their significance at low salt levels.

Findings

Many-body interactions significantly affect melting behavior at low salt.

Good agreement with Yukawa models at high salt, deviations at low salt.

Many-body effects explain differences in melting lines.

Abstract

We study the melting behavior of charged colloidal crystals, using a simulation technique that combines a continuous mean-field Poisson-Boltzmann description for the microscopic electrolyte ions with a Brownian-dynamics simulation for the mesoscopic colloids. This technique ensures that many-body interactions between the colloids are fully taken into account, and thus allows us to investigate how many-body interactions affect the solid-liquid phase behavior of charged colloids. Using the Lindemann criterion, we determine the melting line in a phase-diagram spanned by the colloidal charge and the salt concentration. We compare our results to predictions based on the established description of colloidal suspensions in terms of pairwise additive Yukawa potentials, and find good agreement at high-salt, but not at low-salt concentration. Analyzing the effective pair-interaction between two colloids in a crystalline environment, we demonstrate that the difference in the melting behavior observed at low salt is due to many-body interactions.