Active phase separation by turning towards regions of higher density

Jie Zhang, Ricard Alert, Jing Yan, Ned S. Wingreen, Steve Granick

Research output: Contribution to journalArticlepeer-review

57 Scopus citations


Studies of active matter, from molecular assemblies to animal groups, have revealed two broad classes of behaviour: a tendency to align yields orientational order and collective motion, whereas particle repulsion leads to self-trapping and motility-induced phase separation. Here we report a third class of behaviour: orientational interactions that produce active phase separation. Combining theory and experiments on self-propelled Janus colloids, we show that stronger repulsion on the rear than on the front of these particles produces non-reciprocal torques that reorient particle motion towards high-density regions. Particles thus self-propel towards crowded areas, which leads to phase separation. Clusters remain fluid and exhibit fast particle turnover, in contrast to the jammed clusters that typically arise from self-trapping, and interfaces are sufficiently wide that they span entire clusters. Overall, our work identifies a torque-based mechanism for phase separation in active fluids, and our theory predicts that these orientational interactions yield coexisting phases that lack internal orientational order.

Original languageEnglish (US)
Pages (from-to)961-967
Number of pages7
JournalNature Physics
Issue number8
StatePublished - Aug 2021

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy


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