(464f) Catalytic Motors Near Curved Surfaces: Guided and Trapped Motion

Chemically self-propelled colloidal locomotors are active particles designed to translate along micro- or nanoscale landscapes to deliver various applications, such as micropumping, sensing, drug delivery and cargo transport. In spite of significant enhancements in design and efficiency of catalytic motors, the precise navigation and onboard steering of the colloidal motors still remains as a challenging task. This fact relies on the relative importance of the viscous nature of the medium and the Brownian motion of the particle. Here, we examine the self-diffusiophoresis of a small Janus colloid near a larger stationary solid spherical surface. In the context of self-diffusiophoresis, the colloid itself generates a flow as a result of non-uniform distribution of reactant (or product) solutes due to a chemical reaction taking place asymmetrically on its surface. The dynamics of the Janus particle near a curved no-slip stationary wall that is impenetrable to the solute is found by analytical solution of the solute conservation in conjunction with the application of the Reynolds Reciprocal Theorem of the Stokes flow. It is found that the motions of active particles are influenced not only by hydrodynamic interactions but also via interactions of the solute distribution generated (or consumed) at the surface of the active area of each colloid with the boundary. For deterministic motions, i.e. infinite Péclet numbers, it is observed that the trajectory of the motor depends on two parameters: the colloid active coverage and its relative orientation angle with respect to the wall. For axisymmetric motions, when the active area of the colloid is facing the wall, the motor is repelled by the accumulation of solute in the gap between the swimmer and the wall. For the cases where the cap is opposite to the wall, the swimmer moves towards the wall due to the repulsive interaction of the accumulated solute on the active cap side. In asymmetric incidents on the other hand, the trajectories are more complex as the motor can also rotate due to both hydrodynamic and phoretic interactions with the curved wall. We discuss all possible scenarios for the trajectories of a swimmer approaching obliquely to a curved stationary wall and elucidate the role of hydrodynamic and phoretic interactions on the dynamics of the motor.