Issue 2, 2017

Geometric control of active collective motion

Abstract

Recent experimental studies have shown that confinement can profoundly affect self-organization in semi-dilute active suspensions, leading to striking features such as the formation of steady and spontaneous vortices in circular domains and the emergence of unidirectional pumping motions in periodic racetrack geometries. Motivated by these findings, we analyze the two-dimensional dynamics in confined suspensions of active self-propelled swimmers using a mean-field kinetic theory where conservation equations for the particle configurations are coupled to the forced Navier–Stokes equations for the self-generated fluid flow. In circular domains, a systematic exploration of the parameter space casts light on three distinct states: equilibrium with no flow, stable vortex, and chaotic motion, and the transitions between these are explained and predicted quantitatively using a linearized theory. In periodic racetracks, similar transitions from equilibrium to net pumping to traveling waves to chaos are observed in agreement with experimental observations and are also explained theoretically. Our results underscore the subtle effects of geometry on the morphology and dynamics of emerging patterns in active suspensions and pave the way for the control of active collective motion in microfluidic devices.

Graphical abstract: Geometric control of active collective motion

Supplementary files

Article information

Article type
Paper
Submitted
24 Aug 2016
Accepted
18 Nov 2016
First published
01 Dec 2016

Soft Matter, 2017,13, 363-375

Geometric control of active collective motion

M. Theillard, R. Alonso-Matilla and D. Saintillan, Soft Matter, 2017, 13, 363 DOI: 10.1039/C6SM01955B

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