An axis-asymmetric self-driven micromotor that can perform precession multiplying “on-the-fly” mass transfer

Self-driven micro/nanomotors (MNMs) can generate "on-the-fly" mass transfer, significantly advancing micro/nanofluid technologies. However, the presence of at least one symmetric axis regulates them to implement either translation or rotation, confining the enhancement efficiency for mass transfer. Here, we report axis-asymmetric hollow bowl-shaped Janus micromotors that can perform unusual precession like a spinning top and thus intriguingly enhance liquid medium convection in a large area. They are formed by self-collapse of polystyrene (PS)/platinum (Pt) hollow Janus microspheres adjacent to the boundary between the two hemispheres of PS and Pt caused by the osmotic pressure with the assistance of stirring. The synchronistic self-rotation and translation modulated by the fuel concentration and depression degree can multiply solute mixing and diffusion efficiencies by several times compared with conventional Janus counterparts. This work demonstrates a novel motion mode of self-driven MNMs, precession that greatly enhances micro-convection and rapid diffusion of liquid medium.