(155c) Dynamics of Active Particles Near a Curved Wall: Guided and Trapped Locomotion

Active particles are self-propelling colloidal objects capable of converting energy from their immediate environment into a directed motion. In particular, the presence of a boundary significantly alters the dynamics (and trajectory) of active particles. Here, we investigate the dynamics of an active spherical particle near a curved spherical wall. The particle is actuated by imposing a slip velocity on its surface and its dynamics is governed by a combined analytical-numerical solution relying on the application of low Reynolds number hydrodynamics principles. This approach permits the hydrodynamic interaction of the swimmer and the obstacle to be consistently and accurately calculated in both far and near fields. We focus on two general classes of active particle namely the “squirmer” and the “phoretic" models where the former is a conventional model used for describing the dynamics of biological microswimmers while the latter is a chemo-mechanical transduction mechanism in which a gradient of solute species in the solution brings about particle propulsion. We highlight various types of trajectories and discuss under which circumstances the swimmer can be hydrodynamically trapped or guided. Furthermore, it is explicitly shown how the near field hydrodynamic interactions of the active particle with the obstacle can substantially modify the trajectory of the particle and subsequently brings about various types of trajectories. The analysis also indicates it is always easier to capture an active particle in a closed circular orbit with a larger sized obstacle as in this case the magnitude of the rotational velocity can be sufficiently large so that the particle can adjust its distance and orientation vector with the obstacle. For smaller obstacles, the particle can never be captured. This study can serve as a guide to experimentalists in biomedical engineering, chemistry, materials science and other related disciplines to design and investigate both biological and artificial microswimmers.