Modulation of Non-equilibrium Structures of Active Dipolar Particles by an External Field

TL;DR

This study investigates how external fields influence the self-assembly and polarization of active dipolar particles, revealing complex structural transitions and polarization behaviors driven by the interplay of activity, interactions, and field strength.

Contribution

It introduces a comprehensive simulation analysis of active dipolar particles under external fields, highlighting novel structural phases and polarization responses not previously characterized.

Findings

Disordered fluids of active chains and networks form at low to intermediate fields.

Strong fields induce polarized columnar clusters.

Low activity extends the stability of percolated networks across a range of field strengths.

Abstract

We study the impact of an external alignment field on the structure formation and polarization behavior of low-density dipolar active particles in three dimensions. Performing extensive Brownian dynamics simulations, we characterize the interplay between long-range dipolar interactions, field alignment, and self-propulsion. We find that the competition between activity (favoring bond breaking) and the field's orientational constraint (promoting bond formation) gives rise to a rich variety of self-assembled, actuated structures. At low to intermediate field strengths, disordered fluids composed of active chains and active percolated networks can emerge, whereas strong fields drive the formation of polarized columnar clusters. Counterintuitively, low activity levels significantly extend the range of field strengths over which percolated networks persist. This structural evolution manifests in the polarization response of strongly dipolar systems, which exhibit a transition from super-Langevin to sub-Langevin behavior with increasing activity, as a result of the coupling between structure formation and activity-induced bond breaking.