Entrainment and scattering in microswimmer-colloid interactions

Henry Shum and Julia M. Yeomans
Phys. Rev. Fluids 2, 113101 – Published 9 November 2017

Abstract

We use boundary element simulations to study the interaction of model microswimmers with a neutrally buoyant spherical particle. The ratio of the size of the particle to that of the swimmer is varied from RP/RS1, corresponding to swimmer-tracer scattering, to RP/RS1, approximately equivalent to the swimmer interacting with a fixed, flat surface. We find that details of the swimmer and particle trajectories vary for different swimmers. However, the overall characteristics of the scattering event fall into two regimes, depending on the relative magnitudes of the impact parameter, ρ, and the collision radius, Rcoll=RP+RS. The range of particle motion, defined as the maximum distance between two points on the trajectory, has only a weak dependence on the impact parameter when ρ<Rcoll and decreases with the radius of the particle. In contrast, when ρ>Rcoll the range decreases as a power law in ρ and is insensitive to the size of the particle. We also demonstrate that large particles can cause swimmers to be deflected through large angles. In some instances, this swimmer deflection can lead to larger net displacements of the particle. Based on these results, we estimate the effective diffusivity of a particle in a dilute bath of swimmers and show that there is a nonmonotonic dependence on particle radius. Similarly, we show that the effective diffusivity of a swimmer scattering in a suspension of particles varies nonmonotonically with particle radius.

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  • Received 4 April 2017

DOI:https://doi.org/10.1103/PhysRevFluids.2.113101

©2017 American Physical Society

Physics Subject Headings (PhySH)

Fluid Dynamics

Authors & Affiliations

Henry Shum*

  • Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada

Julia M. Yeomans

  • Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford, OX1 3NP, United Kingdom

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Issue

Vol. 2, Iss. 11 — November 2017

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