Swimming in a Crystal:

TL;DR

This study investigates the behavior of catalytic Janus swimmers and E. coli bacteria within a two-dimensional colloidal crystal, revealing distinct motility patterns and interactions influenced by fuel concentration and crystal structure.

Contribution

It provides new insights into how active particles and bacteria navigate structured environments, highlighting differences in their dynamics and interactions within colloidal crystals.

Findings

Janus swimmers orbit colloids and hop stochastically, with hopping rate inversely related to fuel concentration.

High fuel stabilizes orbits for hundreds of revolutions and causes periodic speed oscillations.

E. coli bacteria are rectified into straight runs within the crystal, unable to turn corners.

Abstract

We study catalytic Janus swimmers and Escherichia coli bacteria swimming in a two-dimensional colloidal crystal. The Janus swimmers orbit individual colloids and hop between colloids stochastically, with a hopping rate that varies inversely with fuel (hydrogen peroxide) concentration. At high fuel concentration, these orbits are stable for 100s of revolutions, and the orbital speed oscillates periodically as a result of hydrodynamic, and possibly also phoretic, interactions between the swimmer and the six neighbouring colloids. Motile E.~coli bacteria behave very differently in the same colloidal crystal: their circular orbits on plain glass are rectified into long, straight runs, because the bacteria are unable to turn corners inside the crystal.