Guiding catalytically active particles with chemically patterned surfaces

TL;DR

This paper demonstrates how chemically patterned surfaces can direct the motion of catalytically active Janus particles by inducing chemi-osmotic flows, enabling controlled docking or stripe-following behaviors.

Contribution

It provides an analytical and numerical study showing how chemical patterning on surfaces can steer active particles via chemi-osmotic flows, a novel control mechanism.

Findings

Particles dock at chemical steps or follow stripes depending on their movement tendencies.

Chemi-osmotic flows can be harnessed to control particle trajectories.

Analytical predictions are confirmed by numerical simulations.

Abstract

Catalytically active Janus particles suspended in solution create gradients in the chemical composition of the solution along their surfaces, as well as along any nearby container walls. The former leads to self-phoresis, while the latter gives rise to chemi-osmosis, providing an additional contribution to self-motility. Chemi-osmosis strongly depends on the molecular interactions between the diffusing chemical species and the wall. We show analytically, using an approximate "point-particle" approach, that by chemically patterning a planar substrate one can direct the motion of Janus particles: the induced chemi-osmotic flows can cause particles to either "dock" at the chemical step between the two materials, or to follow a chemical stripe. These theoretical predictions are confirmed by full numerical calculations. Generically, docking occurs for particles which tend to move away from their catalytic caps, while stripe-following occurs in the opposite case. Our analysis reveals the physical mechanisms governing this behavior.