Cluster formation and phase separation in heteronuclear Janus dumbbells

TL;DR

This study explores how size asymmetry in heteronuclear Janus dumbbells influences their phase behavior, revealing cluster formation, phase separation, and unique geometrical structures, with results aligning qualitatively with experimental observations.

Contribution

It extends previous models by incorporating size asymmetry, demonstrating its impact on phase behavior and structure formation in heteronuclear Janus dumbbells.

Findings

Larger hard-sphere sites promote clustering.

Opposite size asymmetry leads to gas-liquid phase separation.

Symmetric cases exhibit unique geometrical arrangements like lamellae.

Abstract

We have recently investigated the phase behaviour of model colloidal dumbbells constituted by two identical tangent hard spheres, with the first one being surrounded by an attractive square-well interaction (Janus dumbbells, Muna\`o G et al 2014 Soft Matter 10 5269). Here we extend our previous analysis by introducing in the model the size asymmetry of the hard-core diameters, and study the enriched phase scenario thereby obtained. By employing standard Monte Carlo simulations we show that in such "heteronuclear Janus dumbbells" a larger hard-sphere site promotes the formation of clusters, whereas in the opposite condition a gas-liquid phase separation takes place, with a narrow interval of intermediate asymmetries wherein the two phase behaviours may compete. In addition, some peculiar geometrical arrangements, such as lamellae, are observed only around the perfectly symmetric case. A qualitative agreement is found with recent experimental results, where it is shown that the roughness of molecular surfaces in heterogeneous dimers leads to the formation of colloidal micelles.