Abstract

We study the detention statistics of self-propelling droplet microswimmers attaching to microfluidic pillars. These droplets show negative autochemotaxis: they shed a persistent repulsive trail of spent fuel that biases them to detach from pillars in a specific size range after orbiting them just once. We have designed a microfluidic assay recording microswimmers in pillar arrays of varying diameter, derived detention statistics via digital image analysis, and interpreted these statistics via the Langevin dynamics of an active Brownian particle model. By comparing data from orbits with and without residual chemical field, we can independently estimate quantities such as hydrodynamic and chemorepulsive torques, chemical coupling constants and diffusion coefficients, as well as their dependence on environmental factors such as wall curvature. This type of analysis is generalizable to many kinds of microswimmers.

Highlights

  • We study the detention statistics of self-propelling droplet microswimmers attaching to microfluidic pillars

  • For a quantitative estimate of the effects of curvature, wall interaction, and autochemotaxis we model our droplets as active Brownian particles (ABPs) [40,41,42]

  • The extracted torques [Fig. 6(c)] permit a number of observations: both W and − C decrease with pillar size, the latter because orbiting takes longer and the chemorepulsive gradient ∂rc decreases by diffusion, the former possibly because the pusher-type hydrodynamic interactions depend on wall curvature [7]

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Summary

Introduction

We study the detention statistics of self-propelling droplet microswimmers attaching to microfluidic pillars. By comparing data from orbits with and without residual chemical field, we can independently estimate quantities such as hydrodynamic and chemorepulsive torques, chemical coupling constants and diffusion coefficients, as well as their dependence on environmental factors such as wall curvature.

Results
Conclusion

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