Hydrodynamics is Needed to Explain Propulsion in Chemophoretic Colloidal Rafts

TL;DR

This paper demonstrates that hydrodynamics, specifically diffusioosmotic flows, are essential to explain propulsion in chemophoretic colloidal rafts, advancing understanding of active particle dynamics beyond diffusiophoresis alone.

Contribution

The study reveals the critical role of hydrodynamics and diffusioosmotic flows in active colloidal propulsion, which were previously considered secondary.

Findings

Diffusiophoresis explains cluster formation but not propulsion.

Hydrodynamics via diffusioosmotic flows is necessary to account for propulsion.

Hydrodynamic effects significantly influence active colloidal system behavior.

Abstract

Active particles driven by a chemical reaction are the subject of intense research to date due to their rich physics, being intrinsically far from equilibrium, and their multiple technological applications. Recent attention in the field is now shifting towards exploring the fascinating dynamics of mixture of active and passive systems. Here we realize active colloidal rafts, composed of a single catalytic particle encircled by several shells of passive microspheres assembled via light activated, chemophoretic flow. We show that considering only diffusiophoresis can explain the cluster kinetics but not the cluster propulsion behavior. Thus, using the Lorenz reciprocal theorem, we show that propulsion emerges by considering hydrodynamics via the diffusioosmotic answer of the substrate to the generated chemophoretic flow. While diffusioosmotic flows are often relegate to a secondary role, our work demonstrates their importance to understand the rich physics of active catalytic systems.