Hydrodynamic interactions between squirmers near walls: far-field dynamics and near-field cluster stability.

Published version
Repository DOI

Type
Article
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Authors
Théry, A; orcid: 0000-0001-7465-4849 
Maaß, C C; orcid: 0000-0001-6287-4107 
Lauga, E; orcid: 0000-0002-8916-2545 
Abstract

Confinement increases contacts between microswimmers in dilute suspensions and affects their interactions. In particular, boundaries have been shown experimentally to lead to the formation of clusters that would not occur in bulk fluids. To what extent does hydrodynamics govern these boundary-driven encounters between microswimmers? We consider theoretically the symmetric boundary-mediated encounters of model microswimmers under gravity through far-field interaction of a pair of weak squirmers, as well as the lubrication interactions occurring after contact between two or more squirmers. In the far field, the orientation of microswimmers is controlled by the wall and the squirming parameter. The presence of a second swimmer influences the orientation of the original squirmer, but for weak squirmers, most of the interaction occurs after contact. We thus analyse next the near-field reorientation of circular groups of squirmers. We show that a large number of swimmers and the presence of gravity can stabilize clusters of pullers, while the opposite is true for pushers; to be stable, clusters of pushers thus need to be governed by other interactions (e.g. phoretic). This simplified approach to the phenomenon of active clustering enables us to highlight the hydrodynamic contribution, which can be hard to isolate in experimental realizations.

Description
Keywords
Stability, Biofluid mechanics, Propulsion, Active Matter, Low-reynolds-number Flow, Microswimmers
Journal Title
Royal Society open science
Conference Name
Journal ISSN
2054-5703
Volume Title
10
Publisher
Sponsorship
European Research Council (682754)