Soft Matter http://doi.org/5dn (2015)

A droplet brought in contact with a hot-enough plate will develop an insulating vapour layer at the bottom, slowing down further evaporation and making the droplet seem to levitate. This phenomenon — the Leidenfrost effect — is familiar to cooks who sprinkle water on a pan to gauge its temperature.

Cher Lin Tan and colleagues have now demonstrated how this effect might be employed to remove dust and other particles from heated ceramic or metallic surfaces. The physical mechanism is reminiscent of that seen in the self-cleaning ability of highly water-repellent lotus leaves: water droplets rolling along the surface collect and hold dirt particles.

The authors experimented with various types of particles, surfaces and liquids. They found that the temperature-induced lotus-leaf effect is more efficient for water than for ethanol droplets, and that surface roughness doesn't really matter. By adding iron filings to the droplets, they were able to simply magnetically extract the dirt pellet that forms when the liquid within a dirty drop has evaporated. The process may find an application in the mint industry for cleaning coins and recycling precious-metal muck.