Close packing of rods on spherical surfaces

TL;DR

This study investigates the optimal packing arrangements of spherocylindrical rods on spherical surfaces, revealing complex structures and dependencies on particle number and aspect ratio, with implications for colloidal systems.

Contribution

It provides the first detailed analysis of rod packing on spheres, exploring how aspect ratio and particle number influence cluster geometry using simulations.

Findings

Small clusters show diverse geometries depending on aspect ratio.

Larger clusters exhibit disordered or smectic-like arrangements.

Predictions applicable to colloidal rods at emulsion interfaces.

Abstract

We study the optimal packing of short, hard spherocylinders confined to lie tangential to a spherical surface, using simulated annealing and molecular dynamics simulations. For clusters of up to twelve particles, we map out the changes in the geometry of the closest-packed configuration as a function of the aspect ratio $L/D$, where $L$ is the cylinder length and $D$ the diameter of the rods. We find a rich variety of cluster structures. For larger clusters, we find that the best-packed configurations up to around 100 particles are highly dependent on the exact number of particles and aspect ratio. For even larger clusters, we find largely disordered clusters for very short rods ($L/D = 0.25$), while slightly longer rods ($L/D = 0.5$ or $1$) prefer a global baseball-like geometry of smectic-like domains, similar to the behavior of large-scale nematic shells. Our results provide predictions for experimentally realizable systems of colloidal rods trapped at the interface of emulsion droplets.