Geometry-Controlled Relaxation Spectra in Viscoelastic Fluids
Abstract
Soft materials store, dissipate and release mechanical stresses through relaxation processes that often span many orders of magnitude in time. Such relaxation spectra are widely used to infer internal material dynamics and are usually regarded as fingerprints of microscopic complexity, disorder, or heterogeneity. Here we show that a broad relaxation spectrum can instead be generated by the geometry of mechanical excitation itself. Using rotationally driven colloidal dimers in a wormlike micellar fluid with a dominant bulk relaxation time of order one second, we demonstrate that torsional driving converts distance from the driven object into relaxation time. This produces a geometry-controlled hierarchy of relaxation modes: orientational recoils persist for hundreds of seconds and encode past torque protocols over comparably long times. Particle velocimetry reveals rapid angular-momentum transport away from the probe, in contrast to the slow relaxation of stored torsional stress. A continuum shell model captures the observed recoil dynamics and the selective suppression of long-lived contributions under spatial confinement. Our results show that geometry can transform a material with simple intrinsic relaxation into a system with long-lived, space-dependent memory, suggesting a route to tune material dynamics through mechanical excitation rather than composition, with potential implications for microscopic mechanical memory elements.
Related
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BibTeX
@misc{roy2026geometrycontrolled,
title = {{Geometry-Controlled Relaxation Spectra in Viscoelastic Fluids}},
author = {Niloyendu Roy and Rupayan Saha and Debankur Das and Matthias Krüger and Clemens Bechinger},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.18926},
eprint = {2609.18926},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.18926},
}
RIS
TY - UNPB
TI - Geometry-Controlled Relaxation Spectra in Viscoelastic Fluids
AU - Niloyendu Roy
AU - Rupayan Saha
AU - Debankur Das
AU - Matthias Krüger
AU - Clemens Bechinger
PY - 2026
DA - 2026/09/16
PB - arXiv
DO - 10.48550/arxiv.2609.18926
UR - https://arxiv.org/abs/2609.18926
AB - Soft materials store, dissipate and release mechanical stresses through relaxation processes that often span many orders of magnitude in time. Such relaxation spectra are widely used to infer internal material dynamics and are usually regarded as fingerprints of microscopic complexity, disorder, or heterogeneity. Here we show that a broad relaxation spectrum can instead be generated by the geometry of mechanical excitation itself. Using rotationally driven colloidal dimers in a wormlike micellar fluid with a dominant bulk relaxation time of order one second, we demonstrate that torsional driving converts distance from the driven object into relaxation time. This produces a geometry-controlled hierarchy of relaxation modes: orientational recoils persist for hundreds of seconds and encode past torque protocols over comparably long times. Particle velocimetry reveals rapid angular-momentum transport away from the probe, in contrast to the slow relaxation of stored torsional stress. A continuum shell model captures the observed recoil dynamics and the selective suppression of long-lived contributions under spatial confinement. Our results show that geometry can transform a material with simple intrinsic relaxation into a system with long-lived, space-dependent memory, suggesting a route to tune material dynamics through mechanical excitation rather than composition, with potential implications for microscopic mechanical memory elements.
ER -