Femtosecond Laser Processing Enabling Directional Propulsion of Leidenfrost Droplets on Various Material Substrates

Directional propulsion of Leidenfrost droplets is effectively achieved on asymmetric microgroove arrays fabricated via one-step femtosecond laser direct writing. This is realized by simply setting the spacing of the laser scanning lines slightly smaller than the width of a single microgroove during the line-by-line laser scanning process. Because a femtosecond laser can process any given material, this method for driving Leidenfrost droplets is applicable to a wide range of material substrates, as experimentally verified on superhard alloys (magnesium alloy and titanium alloy), semiconductors (monocrystalline silicon and silicon carbide), and ceramics (aluminum nitride, sapphire). The proposed strategy also enables the transport of Leidenfrost droplets on composite surfaces made of different materials as well as the directional propulsion of various volatile liquids. Leveraging the controlled motion of Leidenfrost droplets and the flexible design of surface microstructures via femtosecond laser processing, several applications designed for extremely high-temperature environments have been realized, such as the trapping of Leidenfrost droplets, targeted cooling, self-rotation of Leidenfrost droplets (converting thermal energy into mechanical energy), and electricity generation.