Mesoscale flows in active baths dictate the dynamics of semi-flexible filaments

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Hauptverfasser: Biswas, Bipul, Das, Devadyouti, Kandula, Manasa, Zhou, Shuang
Format: Preprint
Veröffentlicht: 2026
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author Biswas, Bipul
Das, Devadyouti
Kandula, Manasa
Zhou, Shuang
author_facet Biswas, Bipul
Das, Devadyouti
Kandula, Manasa
Zhou, Shuang
contents Semi-flexible filaments in living systems are constantly driven by active forces that often organize into mesoscale coherent flows. Although theory and simulations predict rich filament dynamics, experimental studies of passive filaments in collective active baths remain scarce. Here we present an experimental study on passive colloidal filaments confined to the air-liquid interface beneath a free-standing, quasi-two-dimensional bacterial film featuring jet-like mesoscale flows. By varying filament contour length and bacterial activity, we demonstrate that filament dynamics are governed by its length relative to the characteristic size of the bath. Filaments shorter than the jet width exhibit greatly enhanced translation and rotation with minimal deformation, while long filaments show dramatic deformation but less enhanced transport. We explain our findings through the competition between the active viscous drag of the bath and passive elastic resistance of the filaments, using a modified elastoviscous number that considers the mesoscale flows.
format Preprint
id arxiv_https___arxiv_org_abs_2601_04420
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Mesoscale flows in active baths dictate the dynamics of semi-flexible filaments
Biswas, Bipul
Das, Devadyouti
Kandula, Manasa
Zhou, Shuang
Soft Condensed Matter
Mesoscale and Nanoscale Physics
Statistical Mechanics
Semi-flexible filaments in living systems are constantly driven by active forces that often organize into mesoscale coherent flows. Although theory and simulations predict rich filament dynamics, experimental studies of passive filaments in collective active baths remain scarce. Here we present an experimental study on passive colloidal filaments confined to the air-liquid interface beneath a free-standing, quasi-two-dimensional bacterial film featuring jet-like mesoscale flows. By varying filament contour length and bacterial activity, we demonstrate that filament dynamics are governed by its length relative to the characteristic size of the bath. Filaments shorter than the jet width exhibit greatly enhanced translation and rotation with minimal deformation, while long filaments show dramatic deformation but less enhanced transport. We explain our findings through the competition between the active viscous drag of the bath and passive elastic resistance of the filaments, using a modified elastoviscous number that considers the mesoscale flows.
title Mesoscale flows in active baths dictate the dynamics of semi-flexible filaments
topic Soft Condensed Matter
Mesoscale and Nanoscale Physics
Statistical Mechanics
url https://arxiv.org/abs/2601.04420