Pseudo-Chemotactic Drifts of Artificial Microswimmers

TL;DR

This paper numerically studies artificial microswimmers in fuel gradients, revealing their tendency to drift towards higher concentrations, which is crucial for interpreting experimental results involving chemotactic behaviors.

Contribution

It uncovers the pseudo-chemotactic drift behavior of artificial microswimmers and emphasizes the importance of considering anti-Fickian effects in experimental analysis.

Findings

Microswimmers accumulate in low-concentration regions in steady state.

Swimmers exhibit drift towards high-concentration regions under most conditions.

Interpretation of experimental data must consider anti-Fickian behavior.

Abstract

We numerically investigate the motion of active artificial microswimmers diffusing in a fuel concentration gradient. We observe that, in the steady state, their probability density accumulates in the low-concentration regions, whereas a tagged swimmer drifts with velocity depending in modulus and orientation on how the concentration gradient affects the self-propulsion mechanism. Under most experimentally accessible conditions, the particle drifts toward the high-concentration regions (pseudo-chemotactic drift). A correct interpretation of experimental data must account for such an "anti-Fickian" behavior.