Spontaneously rotating clusters of active droplets

Babak Vajdi Hokmabad, Akinori Nishide, Prashanth Ramesh, Carsten Krueger, Corinna C. Maass*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

19 Citations (Scopus)
38 Downloads (Pure)


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.
Original languageEnglish
Pages (from-to)2731-2741
Number of pages11
JournalSoft matter
Issue number14
Early online date17 Mar 2022
Publication statusPublished - 14 Apr 2022


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