Light-controlled flows in active fluids

Julien Dervaux

doi:10.1038/NPHYS3926

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Light-controlled flows in active fluids

2016-10-31

Julien Dervaux *

Marina Capellazzi Resta

Philippe Brunet

DOI：10.1038/NPHYS3926

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Abstract

En 中文

Many photosynthetic microorganisms are able to detect light and move towards optimal intensities. This ability, known as phototaxis, plays a major role in ecology by affecting natural phytoplankton mass transfers, and has important applications in bioreactor and artificial micro-swimmers technologies. Here we show that this property can be exploited to generate macroscopic fluid flows using a localized light source directed towards shallow suspensions of phototactic microorganisms. Within the intensity range of positive phototaxis, algae accumulate beneath the excitation light, where collective effects lead to the emergence of radially symmetric convective flows. These flows can thus be used as hydrodynamic tweezers to manipulate small floating objects. At high cell density and layer depth, we uncover a new kind of instability, wherein the viscous torque exerted by self-generated fluid flows on the swimmers induces the formation of travelling waves. A model coupling fluid flow, cell concentration and orientation finely reproduces the experimental data.

Keywords:

PATTERN-FORMATION

BIOCONVECTION

SUSPENSIONS

CHEMOTAXIS

PARTICLES

CELLS

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