Structure and Stability of Charged Colloid-Nanoparticle Mixtures

TL;DR

This study investigates how charged nanoparticles affect the structure and phase stability of colloidal suspensions, revealing that increased nanoparticle charge and concentration weaken colloid correlations and can induce melting or aggregation.

Contribution

It provides a molecular dynamics analysis showing how charged nanoparticles destabilize colloidal crystals by enhancing electrostatic screening, a novel insight into colloid-nanoparticle interactions.

Findings

Increasing nanoparticle charge weakens colloid correlations.

Charged nanoparticles can induce melting of colloidal crystals.

Nanoparticles facilitate aggregation through enhanced screening.

Abstract

Physical properties of colloidal materials can be modified by addition of nanoparticles. Within a model of like-charged mixtures of particles governed by effective electrostatic interactions, we explore the influence of charged nanoparticles on the structure and thermodynamic phase stability of charge-stabilized colloidal suspensions. Focusing on salt-free mixtures of particles of high size and charge asymmetry, interacting via repulsive Yukawa effective pair potentials, we perform molecular dynamics simulations and compute radial distribution functions and static structure factors. Analysis of these structural properties indicates that increasing the charge and concentration of nanoparticles progressively weakens correlations between charged colloids. We show that addition of charged nanoparticles to a suspension of like-charged colloids can induce a colloidal crystal to melt and can facilitate aggregation of a fluid suspension due to attractive van der Waals interactions. We attribute the destabilizing influence of charged nanoparticles to enhanced screening of electrostatic interactions, which weakens repulsion between charged colloids. This interpretation is consistent with recent predictions of an effective interaction theory of charged colloid-nanoparticle mixtures.