Femtosecond laser-produced heterogeneous wettability surfaces for turning Leidenfrost drop spinning

Liquid droplets on superheated surfaces produce the Leidenfrost effect. This phenomenon might lead to droplet manipulation and control strategies in microfluidics and thermal management. However, Leidenfrost droplets move randomly and irregularly on superheated surfaces and the manufacturing of special surfaces to control Leidenfrost droplet movement poses great challenges. Here, we propose a simple and environment-friendly method to create heterogeneously wetting surface structures to control the spin motion of droplets on superheated brass using femtosecond laser patterning. The water contact angle of the superhydrophobic area on the surface was ∼160°, and the superhydrophilic area showed ∼7°. A z-shaped pattern was fabricated, which segmented the vapor film and influenced gas flow, and it resulted in the spinning of oval-shaped droplets analogous to a spinning egg. We used simulation to explain this phenomenon and also expanded the application of this droplet control in accelerating dissolution of solids and mechanical driving. This study provides the basis for a creative control method using the Leidenfrost droplet phenomenon, which has broad implications in steam-driven droplet motion and future fluid manipulation.