Self-Assembly of Patchy Colloidal Dumbbells

TL;DR

This study uses Monte Carlo simulations to explore how the shape and size of patchy colloidal dumbbells influence their self-assembled structures, revealing conditions for forming micelles, vesicles, and bilayers.

Contribution

It provides a detailed analysis of how dumbbell size ratio and separation affect self-assembly, offering insights for experimental creation of colloidal vesicles.

Findings

Spherical micelles transition to vesicles with increasing separation at equal sizes.

Size ratio influences the type of structures formed, from micelles to bilayers.

Key parameters identified for experimental fabrication of colloidal vesicles.

Abstract

We employ Monte Carlo simulations to investigate the self-assembly of patchy colloidal dumbbells interacting via a modified Kern-Frenkel potential by probing the system concentration and dumbbell shape. We consider dumbbells consisting of one attractive sphere with diameter $\sigma_1$ and one repulsive sphere with diameter $\sigma_2$ and center-to-center distance $d$ between the spheres. For three different size ratios, we study the self-assembled structures for different separations $l = 2d/(\sigma_1+\sigma_2)$ between the two spheres. In particular, we focus on structures that can be assembled from the homogeneous fluid, as these might be of interest in experiments. We use cluster order parameters to classify the shape of the formed structures. When the size of the spheres is almost equal, $q=\sigma_2/\sigma_1=1.035$, we find that, upon increasing $l$, spherical micelles are transformed to elongated micelles and finally to vesicles and bilayers. For size ratio $q=1.25$ we observe a continuously tunable transition from spherical to elongated micelles upon increasing the sphere separation. For size ratio $q=0.95$ we find bilayers and vesicles, plus faceted polyhedra and liquid droplets. Our results identify key parameters to create colloidal vesicles with attractive dumbbells in experiments.