Natural selection in the colloid world: Active chiral spirals

TL;DR

This paper models natural selection in colloidal systems using active Janus particles forming chiral spirals, revealing how structural reconfiguration and VIP particles influence the stability and evolution of these self-assembled active structures.

Contribution

It introduces a model system demonstrating natural selection principles in colloids and analyzes mechanisms of structural reconfiguration and the role of VIP particles.

Findings

Spiral arms trail the cluster rotation.

Asymmetric arm lengths are tolerated due to self-propulsion.

Structural stability depends on a few VIP particles.

Abstract

We present a model system in which to study natural selection in the colloid world. In the assembly of active Janus particles into rotating pinwheels when mixed with trace amounts of homogeneous colloids in the presence of an AC electric field, broken symmetry in the rotation direction produces spiral, chiral shapes. Locked into a central rotation point by the center particle, the spiral arms are found to trail rotation of the overall cluster. To achieve a steady state, the spiral arms undergo an evolutionary process to coordinate their motion. Because all the particles as segments of the pinwheel arms are self-propelled, asymmetric arm lengths are tolerated. Reconfiguration of these structures can happen in various ways and various mechanisms of this directed structural change are analyzed in detail. We introduce the concept of VIP (very important particles) to express that sustainability of active structures is most sensitive to only a few particles at strategic locations in the moving self-assembled structures.