Confined catalytic Janus swimmers in a crowded channel: geometry-driven rectification transients and directional locking

Self-propelled Janus particles, acting as microscopic vehicles, have the potential of performing complex tasks on a microscopic scale, suitable, e.g., for environmental applications, on-chip chemical information processing or in vivo drug delivery. Development of these smart nano-devices requires a better understanding of how synthetic swimmers move in crowded and confined environments that mimic actual biosystems,e.g.network of blood vessels. Here the dynamics of self-propelled Janus particles interactingwith catalytically passive silica beads in a narrow channel isstudied both experimentally and through numerical simulations. Upon varying the area density of thesilica beads and the width of the channel, active transport reveals a number of intriguing properties, which range from distinct bulk and boundary-free diffusivity at low densities, to directional “locking” and channel “unclogging” at higher densities, whereby a Janus swimmer is capable of transporting large clusters of passive particles.