The role of weak charging in metastable colloidal clusters

TL;DR

This study investigates how weak electrostatic repulsion influences the formation and structure of metastable colloidal clusters, revealing anisotropic charge effects and deviations from simple additive interaction models.

Contribution

It demonstrates the impact of anisotropic surface charge distributions on cluster yields, challenging the assumption of additive isotropic interactions in colloidal systems.

Findings

Cluster yields for sizes 4-6 are lower than expected from theory.

7-membered clusters predominantly form pentagonal bipyramids.

Anisotropic charge distribution affects cluster stability and structure.

Abstract

We study metastable clusters in a colloidal system with competing interactions. A short-ranged polymer-induced attraction drives clustering, while a weak, long-ranged electrostatic repulsion prevents extensive aggregation. We compare experimental yields of cluster structures expected from theory, which assumes simple addition of the competing isotropic interactions. For clusters of size $4\leq m\leq6$, the yield is significantly less than that expected. We attribute this to an anisotropic self-organized surface charge distribution linked to the cluster symmetry: non-additivity of electrostatic repulsion and polymer-induced attraction. 7-membered clusters have a clear optimal yield of the expected pentagonal bipyramid structure as a function of strength of the attractive interaction.