Interfacial bacteria-driven rotation of free-floating active droplets
Abstract
Active droplets provide a platform for converting microscopic propulsion into macroscopic flow. Previous realizations of bacteria-driven droplet rotation typically rely on nearby solid boundaries, external fields, or dense active nematics. Here, we report autonomous rotation of droplets in a three-dimensional aqueous two-phase system driven by interfacial population of \textit{Pseudomonas aeruginosa}. Combining confocal microscopy with fluid particle dynamics simulations, we show that amphiphilic bacteria accumulate at the dextran--polyethylene glycol interface and preferentially move and orient along the local tangent. Interfacial localization partitions the force-free swimming dipole between the two liquid phases, allowing either phase to experience a finite active torque while the combined system remains torque balanced. The simulated interfacial population is more spatially heterogeneous than in the experiments, emphasizing that both the bacterial distribution and its signed orientational organization can influence the instantaneous torque. Over the accessible size range, the macroscopic angular velocity exhibits an inverse-radius (R−1) dependence. We also formulate a theoretical model to rationalize this scaling law, revealing how the macroscopic rotation is governed by collective interfacial swimming and surface coverage. These results identify a fluid-interface-mediated route for converting swimmer activity into macroscopic rotational flow and establish a strategy for harnessing interfacial active matter to regulate droplet dynamics.
Related
- Interfacial dynamics and phase behavior of complex droplets and bubbles
- Wave-driven contraction-deformation coupling enables the motility and revolving waves of active gel droplets
- Vertical motion of a periodically driven floating disc
- Interfacial Faraday instability driven by interspecies-interaction modulation in a phase-separated binary Bose-Einstein condensate
- Stability and Nonlinear Dynamics of Field-Driven Extended Domain Walls with Interfacial Dzyaloshinskii-Moriya Interaction
BibTeX
@misc{yang2026interfacial,
title = {{Interfacial bacteria-driven rotation of free-floating active droplets}},
author = {Dixi Yang and Anheng Wang and Chunming Wang and Hajime Tanaka and Jiaxing Yuan},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.35242},
eprint = {2610.35242},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.35242},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Interfacial bacteria-driven rotation of free-floating active droplets
AU - Dixi Yang
AU - Anheng Wang
AU - Chunming Wang
AU - Hajime Tanaka
AU - Jiaxing Yuan
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2610.35242
UR - https://arxiv.org/abs/2610.35242
AB - Active droplets provide a platform for converting microscopic propulsion into macroscopic flow. Previous realizations of bacteria-driven droplet rotation typically rely on nearby solid boundaries, external fields, or dense active nematics. Here, we report autonomous rotation of droplets in a three-dimensional aqueous two-phase system driven by interfacial population of \textit{Pseudomonas aeruginosa}. Combining confocal microscopy with fluid particle dynamics simulations, we show that amphiphilic bacteria accumulate at the dextran--polyethylene glycol interface and preferentially move and orient along the local tangent. Interfacial localization partitions the force-free swimming dipole between the two liquid phases, allowing either phase to experience a finite active torque while the combined system remains torque balanced. The simulated interfacial population is more spatially heterogeneous than in the experiments, emphasizing that both the bacterial distribution and its signed orientational organization can influence the instantaneous torque. Over the accessible size range, the macroscopic angular velocity exhibits an inverse-radius (R^−1) dependence. We also formulate a theoretical model to rationalize this scaling law, revealing how the macroscopic rotation is governed by collective interfacial swimming and surface coverage. These results identify a fluid-interface-mediated route for converting swimmer activity into macroscopic rotational flow and establish a strategy for harnessing interfacial active matter to regulate droplet dynamics.
ER -