Pair Dispersion in Dilute Suspension of Active Swimmers

Abstract

Ensembles of biological and artificial microswimmers produce long-range velocity fields with strong nonequilibrium fluctuations, which result in dramatic increase diffusivity of embedded particles (tracers). While such enhanced diffusivity may point to enhanced mixing of the fluid, a rigorous quantification of the mixing efficiency requires analysis of pair dispersion of tracers, rather than simple one-particle diffusivity. Here, we calculate analytically the scale-dependent coefficient of relative diffusivity of passive tracers embedded in a dilute suspension of run-and-tumble microswimmers. Although each tracer is subject to strong fluctuations resulting in large absolute diffusivity, the small-scale relative dispersion is suppressed due to the correlations in fluid velocity which are relevant when the inter-tracers separation is below the persistence length of the swimmers motion. Our results suggest that the reorientation of swimming direction plays an important role in biological mixing and should be accounted in design of potential active matter devices capable of effective fluid mixing at microscale.

arXiv comment9 pages, 3 figures

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Cited by in corpus (5)

• On the Einstein relation between mobility and diffusion coefficient in an active bath
• Swimming suppresses correlations in dilute suspensions of pusher microorganisms
• Time-dependent properties of run-and-tumble particles: Density relaxation
• Tracer dynamics in an interacting active bath: fluctuations and energy partition
• Harmonic chain driven by active Rubin bath: transport properties and steady-state correlations