Geometrical entanglement and alignment regulate self-organization in active ring polymer suspensions

TL;DR

This study investigates how geometrical entanglement and orientational order influence self-organization in active ring polymer suspensions, revealing a non-monotonic relationship between activity, entanglement, and alignment.

Contribution

It introduces the wrapping number as a novel measure of entanglement and shows how it, along with alignment, governs self-organization in active ring systems.

Findings

Moderate entanglement stabilizes aligned ring contacts.

Excessive entanglement disrupts alignment.

Self-organization depends non-monotonically on activity-induced entanglement.

Abstract

We study the emerging self-organization in active ring suspensions, focusing on how the rings' orientational order and geometric entanglement vary with density and spatial confinement. To quantify entanglement, we introduce the wrapping number, a pairwise measure of ring interpenetration, while orientational order is characterized by the alignment of the normal vectors to the rings' osculating planes. Both wrapping number and alignment distinguish active from passive systems, and their combination aptly identifies the self-organized states that emerge with the onset of activity. Mutual-information analysis reveals a significant correlation between alignment and wrapping number across all considered active conditions. However, self-organization displays a non-monotonic dependence on the activity-induced entanglement. Specifically, moderate wrapping stabilizes contacts of neighboring aligned rings, while excessive entanglement disrupts alignment. We show that this competition arises because increasing entanglement interferes with the planar conformations required to form aligned stacks. Given the simplicity of this microscopic mechanism, analogous effects may occur more generally in polymer systems where the degree of entanglement is regulated by out-of-equilibrium effects.