Confinement-induced transitions in the dynamics of self-diffusiophoretic microswimmer under Poiseuille flow

The dynamics of artificial microswimmers in confined flows remain poorly understood despite their relevance to microfluidics, drug delivery, and the navigation of active particles through physiological pathways. Here, we investigate the self-diffusiophoretic motion of spherical Janus particles in pressure-driven Poiseuille flow within microchannels, systematically spanning the weak to strong confinement regime. Using bispherical eigenfunction expansions for the solute and flow fields, we analyze swimmer-boundary interactions in weak to moderate confinement, while complementary finite-element simulations are employed to examine the strongly confined regime without invoking artificial steric potentials. Our analysis reveals that confinement fundamentally reshapes swimmer trajectories: near-wall equilibria characteristic of weak confinement is destroyed, giving rise to centerline attractors, oscillatory states with confinement-dependent wavelengths. Furthermore, the non-trivial coupling between diffusiophoretic slip, hydrodynamic interactions with opposing walls, and the curvature of Poiseuille flow yields striking modifications of trajectories, including confinement-induced transitions from centerline to wall-bound states. These results demonstrate that strongly confined environments cannot be captured by far-field or weak-confinement theories, and they emphasize the essential role of geometric confinement in dictating active particle transport. Beyond providing physical insight into the interplay between chemical activity, hydrodynamics, and flow curvature, our findings further establish design principles for the controlled deployment of microswimmers in narrow fluidic passages of technological and biomedical significance.