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Setting the pace of microswimmers: when increasing viscosity speeds up self-propulsion

Pande, Jayant; Merchant, Laura; Krüger, Timm; Harting, Jens; Smith, Ana-Sunčana (2017) Setting the pace of microswimmers: when increasing viscosity speeds up self-propulsion. New journal of physics, 19 . ISSN 1367-2630

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Abstract

It has long been known that some microswimmers seem to swim counter-intuitively faster when the viscosity of the surrounding fluid is increased, whereas others slow down. This conflicting dependence of the swimming velocity on the viscosity is poorly understood theoretically. Here we explain that any mechanical microswimmer with an elastic degree of freedom in a simple Newtonian fluid can exhibit both kinds of response to an increase in the fluid viscosity for different viscosity ranges, if the driving is weak. The velocity response is controlled by a single parameter Gamma, the ratio of the relaxation time of the elastic component of the swimmer in the viscous fluid and the swimming stroke period. This defines two velocity-viscosity regimes, which we characterize using the bead-spring microswimmer model and analyzing the different forces acting on the parts of this swimmer. The analytical calculations are supported by lattice-Boltzmann simulations, which accurately reproduce the two velocity regimes for the predicted values of Gamma.

Item Type: Article
Uncontrolled Keywords: microswimming ; anomalous increase in velocity ; analytical modeling ; lattice-Boltzmann simulations
Subjects: NATURAL SCIENCES > Mathematics
Divisions: Division of Physical Chemistry
Depositing User: Ana Sunčana Smith
Date Deposited: 18 Jan 2018 15:28
Last Modified: 18 Jan 2018 15:30
URI: http://fulir.irb.hr/id/eprint/3834
DOI: 10.1088/1367-2630/aa6e3a

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