Isotropically active colloids under uniform force fields: from forced to spontaneous motion
File(s)
Accepted version
Author(s)
Saha, Saikat
Yariv, Ehud
Schnitzer, Ory
Type
Journal Article
Abstract
We consider the inertia-free motion of an isotropic chemically active particle which is exposed to a weak uniform force field. This problem is characterised by two velocity scales, a ‘chemical’ scale associated with diffusio-osmosis and a ‘mechanical’ scale associated with the external force. The motion animated by the force deforms the originally spherically symmetric solute cloud surrounding the particle, thus resulting in a concomitant diffusio-osmotic flow which, in turn, modifies the particle speed. A weak-force linearisation furnishes a closed-form expression for the particle velocity as a function of the intrinsic Péclet number α associated with the chemical velocity scale. We find that the predicted velocity may become singular at α=4, and that this happens under the same conditions on the surface parameters for which the associated unforced problem is known to exhibit, for α>4, a symmetry-breaking instability giving rise to steady spontaneous motion (Michelin, Lauga & Bartolo, Phys. Fluids, vol. 25, 2013, 061701). Here, a local analysis in a distinguished region near α=4, wherein the velocity scaling is amplified, yields a closed-form description of the imperfect bifurcation which bridges between a perturbed stationary state and a perturbed spontaneous motion. Remarkably, while the direction of spontaneous motion in the absence of an external force is random, in the perturbed case that motion is rendered steady solely in the directions parallel or antiparallel to the external force.
Date Issued
2021-04-14
Date Acceptance
2021-04-01
Citation
Journal of Fluid Mechanics, 2021, 916, pp.1-19
ISSN
0022-1120
Publisher
Cambridge University Press
Start Page
1
End Page
19
Journal / Book Title
Journal of Fluid Mechanics
Volume
916
Copyright Statement
© The Author(s), 2021. Published by Cambridge University Press.
This article has been published in a revised form in Journal of Fluid Mechanics https://doi.org/10.1017/jfm.2021.222. This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative works.
This article has been published in a revised form in Journal of Fluid Mechanics https://doi.org/10.1017/jfm.2021.222. This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative works.
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000639952600001&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Subjects
Science & Technology
Technology
Physical Sciences
Mechanics
Physics, Fluids & Plasmas
Physics
active matter
coupled diffusion and flow
Publication Status
Published
Article Number
ARTN A47
Date Publish Online
2021-04-14