Reversibility, Chaos, and Attractors in Periodically Sheared Elastic Filaments

TL;DR

This study explores how elastic filaments under oscillatory shear exhibit complex dynamics including reversibility loss, chaos, and multiple attractors, combining experiments and simulations to reveal stochastic symmetry breaking and intermittency.

Contribution

It introduces a combined experimental and numerical analysis of elastic filaments under oscillatory shear, revealing new dynamical regimes and attractor behaviors in soft matter systems.

Findings

Irreversibility emerges at longer oscillation periods due to flow and thermal noise.

Filaments cycle between straight and buckled shapes with phase shifts, showing coexistence of attractors.

Noise induces spontaneous switching between attractors, leading to intermittency.

Abstract

The dynamics of filaments in flow are central to understanding a wide range of biological and soft-matter systems, yet their behavior under time-dependent forcing remains poorly understood. Here, we investigate the long-time dynamics of Brownian inextensible elastic filaments subjected to strong uniform oscillatory shear by combining microfluidic experiments on actin filaments with numerical simulations based on a fluctuating Euler-Bernoulli elastica model in a viscous fluid. As the oscillation period increases, irreversibility emerges from the interplay of flow-induced deformations and thermal noise. This leads to a departure from reversible, deterministic rigid-body dynamics: in this regime, the filaments cycle between nearly straight, flow-aligned conformations at full periods and buckled shapes at half periods. Owing to the time-glide symmetry of the system, two such attracting states in fact coexist with a phase shift of half a period. The system spontaneously selects one, but occasionally switches between them as a result of noise, producing intermittent transitions between apparent order and disorder. This system constitutes an experimentally accessible realization of stochastic symmetry breaking, attractor hopping, and intermittency in a minimal nonequilibrium soft-matter system, with novel implications for the design and control of soft matter systems under time-dependent flows.