Fig. 4: Applications of the tailoring Leidenfrost film.

a–d Droplet steam engine. a, b Photographs of the droplet steam engine. The droplet steam engine consists of a heater with a chemically heterogeneous surface, a gear, and a force transmission device to connect the drop and the gear. c Working process of the droplet steam engine. When water is added, the generated vapor actuates the water drop rotating, which in turn drives the steam engine to work. d Curve of the steam engine speed as a function of time. After adding a 100-μl drop, the steam engine can rotate for nearly 40 s. e–h Shaft driving in a narrow gap. e Structure of the shaft driving device. f Illustration of the shaft driving strategy. Water injection results in a torque acting on the upper shaft, and thus rotates the shaft. g Images of the shaft driving process. The distance between the shaft and the heating pillar is 1 mm. The shaft starts to rotate after the injection of water (the middle image), while the rotation ceases when stopping the injection (the right image). h Rotating speed of shaft versus time. The rotating speed of the shaft is about 130 rpm, which decreases to zero within 5 s after stopping water injection (9 s), while re-injecting water (16 s) causes the shaft to return to about 130 rpm within 8 s. The red arrows indicate the rotation directions of the shaft. i–j Directional transport of drops using a planar hot surface. i Illustration of the directional transport of a drop on a superhydrophobic surface with a “herringbone” superhydrophilic pattern. j Time-lapse trajectory of a drop on the hot pattern surface. k Anti-gravity propulsion of a drop on a 5-degree inclined surface. The temperature of the surfaces is 135 °C. The volume of drops in (j, k) is 60 μl. The red arrows indicate the motion directions of the drops.