Low-Friction Self-Centering Droplet Propulsion and Transport Using a Leidenfrost Herringbone-Ratchet Structure

The Leidenfrost phenomenon (as when a bead of water skates atop trapped steam across a hot griddle) receives much interest for transporting droplets with low friction. While linear motion is eased by low friction, changing direction becomes difficult, without constraint by walls. The authors use the concept of negative feedback by design of substrate structure to achieve transport along complex pathways, without walls. These paths furthermore allow control of a droplet's position, while maintaining speed and low friction. The intrinsic self-centering and correction via negative feedback offers exciting potential for designing complex paths and tracks for levitated droplets to follow.