Hydrodynamic instabilities of activity-balanced binary suspensions

Abstract: Microorganisms living in microfluidic environments often form multispecies swarms, where they can leverage collective motions to achieve enhanced transport and spreading. Nevertheless, there is a general lack of physical understandings of the origins of the multiscale unstable dynamics observed within these systems. In this study, we build a theoretical model to study the hydrodynamic instabilities arising in a dilute mixture of microswimmers that have different propulsion mechanisms and populations. Especially, we consider the scenario of an “activity-balanced” binary suspension that produces zero mean extra stress. We construct a continuum kinetic model that describes the transient dynamics as the system deviates from uniform isotropy. We perform linear stability analyses to show that such binary active suspensions may exhibit rich instability behavior that are far more complex than the single-species cases (e.g., pure pusher or puller suspensions) that have been well studied.

Recommended citation: Bryce Palmer, Wen Yan, Tong Gao. "Hydrodynamic instabilities of activity-balanced binary suspensions." Physical Review Fluids, June 21, 2022.
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