Quadrupolar active stress induces exotic phases of defect motion in active nematics

TL;DR

This study explores how quadrupolar active stresses influence the self-organization and defect dynamics in active nematics, revealing new phases and defect arrangements driven by these higher-order stresses.

Contribution

It introduces the role of quadrupolar active stresses in active nematics, demonstrating their ability to induce novel defect motions and self-organized structures not seen with dipolar stresses alone.

Findings

Quadrupolar stresses stabilize certain active nematic patterns.

Emergence of polar and nematic defect orderings.

Formation of defect chains and asters.

Abstract

A wide range of living and artificial active matter exists in close contact with substrates and under strong confinement, where in addition to dipolar active stresses, quadrupolar active stresses can become important. Here, we numerically investigate the impact of quadrupolar non-equilibrium stresses on the emergent patterns of self-organisation in non-momentum conserving active nematics. Our results reveal that beyond having stabilising effects, the quadrupolar active forces can induce various modes of topological defect motion in active nematics. In particular, we find the emergence of both polar and nematic ordering of the defects, as well as new phases of self-organisation that comprise topological defect chains and topological defect asters. The results contribute to further understanding of emergent patterns of collective motion and non-equilibrium self-organisation in active matter.