Active dipole clusters: from helical motion to fission

TL;DR

This paper investigates how active self-propulsion affects the dynamics and structure of dipolar particle clusters, revealing complex behaviors like helical motion and fission depending on propulsion protocols.

Contribution

It introduces a numerical study of active dipole clusters showing how self-propulsion induces diverse cluster dynamics and structural transformations.

Findings

Cluster center-of-mass follows a helical path influenced by initial magnetization.

Rapid increase in self-propulsion causes cluster fission.

Slow increase in self-propulsion prevents cluster fission.

Abstract

The structure of a finite particle cluster is typically determined by total energy minimization. Here we consider the case where a cluster of soft sphere dipoles becomes active, i.e. when the individual particles exhibit an additional self-propulsion along their dipole moments. We numerically solve the overdamped equations of motion for soft-sphere dipoles in a solvent. Starting from an initial metastable dipolar cluster, the self-propulsion generates a complex cluster dynamics. The final cluster state has in general a structure widely different to the initial one, the details depend on the model parameters and on the protocol of how the self-propulsion is turned on. The center-of-mass of the cluster moves on a helical path, the details of which are governed by the initial cluster magnetization. An instantaneous switch to a high self-propulsion leads to fission of the cluster. However, fission does not occur if the self-propulsion is increased slowly to high strengths. Our predictions can be verified through experiments with self-phoretic colloidal Janus-particles and for macroscopic self-propelled dipoles in a highly viscous solvent.