How walls affect the dynamics of self-phoretic microswimmers

TL;DR

This paper investigates how a nearby planar wall influences the motion of self-phoretic microswimmers, revealing diverse behaviors such as bound states and scattering, driven by asymmetric surface catalysis and wall interactions.

Contribution

It provides a detailed analysis of wall effects on self-phoretic microswimmers, highlighting behaviors not predictable by hydrodynamic models alone.

Findings

Identification of bound states near walls due to wall-phoretic effects

Demonstration of scattering trajectories where swimmers move away from walls

Development of a phase diagram characterizing swimmer behaviors near walls

Abstract

We study the effect of a nearby planar wall on the propulsion of a spherical phoretic micro-swimmer driven by reactions on its surface. An asymmetric coverage of catalysts on its surface which absorb reactants and generate products gives rise to an anisotropic interfacial flow that propels the swimmer. We analyse the near-wall dynamics of such a self-phoretic swimmer as a function of the asymmetric catalytic coverage of the surface. By an analysis of the fundamental singularities of the flow and concentration or electrostatic potential gradients generated we are able to obtain and rationalise a phase diagram of behaviours as a function of the characteristics of the swimmer surface. We find a variety of possible behaviours, from "bound states" where the swimmer remains near the wall to "scattering" or repulsive trajectories in which the swimmer ends far from the wall. The formation of some of the bound states is a purely wall-phoretic effect and cannot be obtained by simply mapping a phoretic swimmer to a hydrodynamic one.