Active colloidal rafts perform swimming strokes that propel their host droplets
Abstract
Active particles confined in droplets can set their host droplet into motion. This phenomenon is usually attributed to direct hydrodynamic forcing by the enclosed particles. Here we reveal a different mechanism: we show that a self-propelled raft of active colloids confined in a thin oil droplet at the surface of water typically follows an off-centered orbit, thus periodically deforming the droplet's contact line in an anisotropic way. This non-reciprocal deformation acts as a swimming stroke and propels the droplet according to the principles of low-Reynolds-number swimming. The effect is absent for a single colloid and arises from the intrinsically many-body dynamics of the raft, which we capture with a dynamical model coupling viscous hydrodynamics and many-body active dynamics. Our results show how collective internal activity can be converted into locomotion through deformation of a soft confining boundary.
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BibTeX
@misc{kato2026active,
title = {{Active colloidal rafts perform swimming strokes that propel their host droplets}},
author = {Airi N. Kato and Julien Brémont and Etienne Harté and Jean-Michel Rampnoux and Jean-François Joanny and Hamid Kellay},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.21963},
eprint = {2609.21963},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.21963},
}
RIS
TY - UNPB
TI - Active colloidal rafts perform swimming strokes that propel their host droplets
AU - Airi N. Kato
AU - Julien Brémont
AU - Etienne Harté
AU - Jean-Michel Rampnoux
AU - Jean-François Joanny
AU - Hamid Kellay
PY - 2026
DA - 2026/09/18
PB - arXiv
DO - 10.48550/arxiv.2609.21963
UR - https://arxiv.org/abs/2609.21963
AB - Active particles confined in droplets can set their host droplet into motion. This phenomenon is usually attributed to direct hydrodynamic forcing by the enclosed particles. Here we reveal a different mechanism: we show that a self-propelled raft of active colloids confined in a thin oil droplet at the surface of water typically follows an off-centered orbit, thus periodically deforming the droplet's contact line in an anisotropic way. This non-reciprocal deformation acts as a swimming stroke and propels the droplet according to the principles of low-Reynolds-number swimming. The effect is absent for a single colloid and arises from the intrinsically many-body dynamics of the raft, which we capture with a dynamical model coupling viscous hydrodynamics and many-body active dynamics. Our results show how collective internal activity can be converted into locomotion through deformation of a soft confining boundary.
ER -