Equilibrium clusters in suspensions of colloids interacting via potentials with a local minimum

TL;DR

This paper demonstrates through simulations that colloidal potentials with a local minimum and a repulsive tail can form equilibrium clusters, bridging known cluster-forming mechanisms.

Contribution

It introduces a new class of potentials capable of generating equilibrium clusters, expanding understanding of colloidal self-assembly mechanisms.

Findings

Potential with local minimum can form clusters.

Cluster shape varies with density and potential type.

Assembly driven by entropy at low density, energy at high density.

Abstract

In simple colloidal suspensions, clusters are various multimers that result from colloid self-association and exist in equilibrium with monomers.There are two types of potentials that are known to produce clusters: a) potentials that result from the competition between short-range attraction and long-range repulsion and are characterized by a global minimum and a repulsive tail and b) purely repulsive potentials which have a soft shoulder. Using computer simulations, we demonstrate in this work that potentials with a local minimum and a repulsive tail, not belonging to either of the known types, are also capable of generating clusters. A detailed comparative analysis shows that the new type of cluster-forming potential serves as a bridge between the other two. The new clusters are expanded in shape and their assembly is driven by entropy, like in the purely repulsive systems but only at low density. At high density, clusters are collapsed and stabilized by energy, in common with the systems with competing attractive and repulsive interactions.