Orientation-dependent self-diffusiophoresis of a Janus particle near a planar wall

We study the self-diffusiophoretic motion of a Janus particle near a planar wall, with a focus on the influence of particle orientation on propulsion. Our analysis focuses on a spherical particle that is predominantly coated with a catalytic material, a configuration predicted to lead to distinctive near‑wall dynamics. While far-field analytical approaches and numerical methods have been used to study such particles, they face challenges in the extreme near-wall regime, where geometric confinement and steep solute concentration gradients demand fine resolution or high‑order computations. We address this limitation through an asymptotic analysis in the near-contact limit, where the gap between the particle and the wall is small and the inert region is asymptotically comparable in size to the lubrication region. In this distinguished limit, a detailed analysis of the boundary between the catalytic and inert regions is required to resolve the solute concentration, the resulting force, and the particle velocity. The near-wall dynamics exhibit strong sensitivity to orientation, with qualitatively different behavior arising when the catalytic cap faces toward or away from the wall. The analytical results will be compared to numerical solutions for validation.