Diffusion-based height analysis reveals robust microswimmer-wall separation

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.

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• Activity-induced microswimmer interactions and cooperation in one-dimensional environments
• Log it: How to fit an active Brownian particle's mean squared displacement with improved parameter estimation
• Tracking Janus microswimmers in 3D with Machine Learning
• Height Distribution and Orientation of Colloidal Dumbbells Near a Wall
• Influence of PEG on the Clustering of Active Janus Colloids
• Autophoresis of a Janus particle near a planar wall: a lubrication limit