Hydrodynamically induced particle drift near corrugated surfaces

We present an experimental and theoretical study of the sedimentation of spheres nearby corrugated surfaces, whose grooves are tilted with respect to the gravitational force. Our experiments show oscillatory, or zigzag, particle trajectories and an overall drift along the surface grooves. We develop an analytical perturbation theory for the hydrodynamic interactions between the sedimenting sphere and the corrugated surface and find agreement between our theory and experiments. The theoretical predictions further reveal that the interactions of the flows induced by the particle motion with the surface shapes generate local pressure gradients, which explain the observed oscillatory dynamics. Additionally, we demonstrate that this behavior is generic for various surface shapes, including rectangular, sinusoidal, and triangular grooves. Finally, we theoretically and experimentally quantify the particle drift as a function of the shape and wavelength of the corrugations and the particle size to identify the parameters which lead to an optimal transport of the particles.