Autophoresis of a Janus particle near a planar wall: a lubrication limit

TL;DR

This paper develops an asymptotic analysis for the self-diffusiophoresis of Janus particles near a wall, revealing how particle orientation influences propulsion and stability in the near-contact lubrication limit.

Contribution

It introduces a lubrication limit asymptotic approach to analyze particle propulsion and orientation stability near a wall, addressing numerical challenges in extreme confinement.

Findings

Particle orientation affects propulsion direction.

Capsize determines rotational stability.

Analysis extends to tilted orientations.

Abstract

We study the self-diffusiophoresis of a spherical chemically active particle near a planar, impermeable wall, with a focus on the influence of particle orientation on propulsion. We analyze a Janus particle with asymmetric surface chemical activity, consisting of a small inert region within a catalytically active cap. While numerical simulations have been used to study such particles, they encounter difficulties resolving the flow and transport in the extreme near-wall regime due to geometric confinement and steep solute concentration gradients. We address this limitation through an asymptotic analysis in the near-contact limit, where the gap between the particle and the wall is narrow. In particular, we consider the distinguished limit in which the inert region is asymptotically comparable in size to the lubrication region. We analyze an axisymmetric configuration in which the inert face is oriented parallel to the wall and extend the analysis to slightly tilted orientations. We find that the capsize determines whether a tilted particle rotates back toward the axisymmetric state or continues to reorient, thereby characterizing its rotational stability in the near-contact regime.