Fast droplet mixing via a Leidenfrost reactor

Under the Leidenfrost effect, a droplet levitates on a vapour cushion fed by evaporation of the liquid. The vapour layer insulates and lifts the droplet off the surface, allowing it to levitate in a long-lived, non-wetting and ultramobile state. This work finds the convective internal swirls within a Leidenfrost droplet greatly enhance droplet mixing, reducing mixing time by over 100-fold compared to pure diffusion at room temperature. Our model reveals that the mixing time of a self-propelling droplet, on an asymmetrically grooved surface, mainly depends on the droplet shape and the groove parameters. Experimental results align closely with the model predictions. Additionally, we show that using channel walls enables propulsion of large droplet slugs or streams, which occupy the entire ring channel with volumes up to 2.9 mL. These findings open new opportunities for advancing microfluidics and process intensification. © 2025 The Author(s)