Issue 30, 2020

Snapping elastic disks as microswimmers: swimming at low Reynolds numbers by shape hysteresis

Abstract

We illustrate a concept for shape-changing microswimmers, which exploits the hysteresis of a shape transition of an elastic object, by an elastic disk undergoing cyclic localized swelling. Driving the control parameter of a hysteretic shape transition in a completely time-reversible manner gives rise to a non-time-reversible shape sequence and a net swimming motion if the elastic object is immersed into a viscous fluid. We prove this concept with a microswimmer which is a flat circular elastic disk that undergoes a transition into a dome-like shape by localized swelling of an inner disk. The control parameter of this shape transition is a scalar swelling factor of the disk material. With a fixed outer frame with an additional attractive interaction in the central region, the shape transition between flat and dome-like shape becomes hysteretic and resembles a hysteretic opening and closing of a scallop. Employing Stokesian dynamics simulations of a discretized version of the disk we show that the swimmer is effectively moving into the direction of the opening of the dome in a viscous fluid if the swelling parameter is changed in a time-reversible manner. The swimming mechanism can be qualitatively reproduced by a simple 9-bead model.

Graphical abstract: Snapping elastic disks as microswimmers: swimming at low Reynolds numbers by shape hysteresis

Article information

Article type
Paper
Submitted
24 Apr 2020
Accepted
30 Jun 2020
First published
08 Jul 2020
This article is Open Access
Creative Commons BY license

Soft Matter, 2020,16, 7088-7102

Snapping elastic disks as microswimmers: swimming at low Reynolds numbers by shape hysteresis

C. Wischnewski and J. Kierfeld, Soft Matter, 2020, 16, 7088 DOI: 10.1039/D0SM00741B

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