Issue 14, 2022

Spontaneously rotating clusters of active droplets


We report on the emergence of spontaneously rotating clusters in active emulsions. Ensembles of self-propelling droplets sediment and then self-organise into planar, hexagonally ordered clusters which hover over the container bottom while spinning around the plane normal. This effect exists for symmetric and asymmetric arrangements of isotropic droplets and is therefore not caused by torques due to geometric asymmetries. We found, however, that individual droplets exhibit a helical swimming mode in a small window of intermediate activity in a force-free bulk medium. We show that by forming an ordered cluster, the droplets cooperatively suppress their chaotic dynamics and turn the transient instability into a steady rotational state. We analyse the collective rotational dynamics as a function of droplet activity and cluster size and further propose that the stable collective rotation in the cluster is caused by a cooperative coupling between the rotational modes of individual droplets in the cluster.

Graphical abstract: Spontaneously rotating clusters of active droplets

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Article information

Article type
21 Dec 2021
09 Mar 2022
First published
17 Mar 2022
This article is Open Access
Creative Commons BY license

Soft Matter, 2022,18, 2731-2741

Spontaneously rotating clusters of active droplets

B. V. Hokmabad, A. Nishide, P. Ramesh, C. Krüger and C. C. Maass, Soft Matter, 2022, 18, 2731 DOI: 10.1039/D1SM01795K

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