Diffusion-Based Height Analysis Reveals Robust Microswimmer-Wall Separation

Physical Review Letters, vol. 125, pp. 238001

Abstract

Microswimmers typically move near walls, which can strongly influence their motion. However, direct experimental measurements of swimmer-wall separation remain elusive to date. Here, we determine this separation for model catalytic microswimmers from the height dependence of the passive component of their mean-squared displacement. We find that swimmers exhibit "ypsotaxis," a tendency to assume a fixed height above the wall for a range of salt concentrations, swimmer surface charges, and swimmer sizes. Our findings indicate that ypsotaxis is activity induced, posing restrictions on future modeling of their still-debated propulsion mechanism.

Authors 3

1. Stefania Ketzetzi Aachen Soft Matter Physics Huygens-Kamerlingh Onnes Laboratory

   Leiden University

   Affiliation as printed

   Soft Matter Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, Netherlands

2. Joost de Graaf

   Utrecht University

   Affiliation as printed

   Institute for Theoretical Physics, Center for Extreme Matter and Emergent Phenomena, Utrecht University, Princetonplein 5, 3584 CC Utrecht, Netherlands

3. Daniela J. Kraft Aachen Soft Matter Physics Huygens-Kamerlingh Onnes Laboratory

   Leiden University

   Affiliation as printed

   Soft Matter Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, Netherlands