Self-propulsion of a catalytically active particle near a planar wall: from reflection to sliding and hovering

TLDR

Micron‑sized particles that move via self‑generated chemical gradients are model systems for active matter and promise applications that require robust environmental sensing and response. The study predicts that a catalytically active Janus particle near a hard planar wall can either reflect, hover, or move at a steady orientation and height, and shows that such behavior can be selected by tuning surface chemistry. These behaviors arise from the particle’s self‑generated hydrodynamic and chemical fields interacting with the wall, and can be controlled by adjusting catalyst coverage and solute–surface interactions. The steady‑state height and orientation depend on catalyst coverage and solute interactions, confirming that reflection, hovering, and steady sliding are attainable by appropriate surface design.

Abstract

Micron-sized particles moving through solution in response to self-generated chemical gradients serve as model systems for studying active matter. Their far-reaching potential applications will require the particles to sense and respond to their local environment in a robust manner. The self-generated hydrodynamic and chemical fields, which induce particle motion, probe and are modified by that very environment, including confining boundaries. Focusing on a catalytically active Janus particle as a paradigmatic example, we predict that near a hard planar wall such a particle exhibits several scenarios of motion: reflection from the wall, motion at a steady-state orientation and height above the wall, or motionless, steady "hovering." Concerning the steady states, the height and the orientation are determined both by the proportion of catalyst coverage and the interactions of the solutes with the different "faces" of the particle. Accordingly, we propose that a desired behavior can be selected by tuning these parameters via a judicious design of the particle surface chemistry.