Shape anisotropy governs organization of active rods: Swarming, turbulence, flocking, and jamming

TL;DR

This study explores how shape anisotropy influences self-organization in active rods, revealing diverse collective behaviors and providing insights for designing synthetic active materials.

Contribution

It combines experiments and simulations to show how aspect ratio and density control emergent behaviors in active rods, advancing understanding of biological and synthetic microswimmer organization.

Findings

Varying aspect ratio and density induces transitions from Brownian motion to flocking and jamming.

Spatiotemporal analysis reveals giant-number fluctuations across different states.

The minimal model offers insights into biological microswimmer organization and material design.

Abstract

Shape anisotropy of individual building blocks plays a crucial role in creating exotic structures and controlling phase behavior in equilibrium systems. We present a combined experimental and simulation study in which we used light-driven self-propelled rods to investigate when and how shape-induced alignment and steric and hydrodynamic interactions govern self-organization. Varying rod aspect ratio and area fraction causes the system to evolve from active Brownian motion to swarming, active turbulence, flocking, large clusters, and jamming. A state diagram summarizes emergent behaviors, and spatiotemporal analyses reveal distinct giant-number fluctuations across states. This minimal model offers insight into the self-organization of biological rodlike microswimmers, enabling the decoupling of physical from biological mechanisms. Our results provide design rules for programmable synthetic active materials and highlight parallels with bacterial swarms and other biological assemblies.