Droplets bouncing off surfaces are an everyday phenomenon, like raindrops bouncing off lotus leaves or water drops sizzling in a hot pan, levitating and sliding around—aka the Leidenfrost effect. There is also an inverse Leidenfrost effect, first described in 1969, that involves a hot object such as a droplet levitating above a cold surface. Understanding the mechanisms behind these phenomena is crucial to a broad range of practical applications, such as self-cleaning, anti-icing, anti-fogging, surface charge printing, or droplet-based logic systems.

Droplets usually only bounce if the surface is superheated or engineered in some way to reduce stickiness. Physicists from the City University of Hong Kong have figured out how to achieve this bouncing behavior of hot oil droplets off almost any surface, according to a new paper published in the journal Newton.

As we've reported previously, in 1756, a German scientist named Johann Gottlob Leidenfrost reported his observation of the unusual phenomenon. Normally, he noted, water splashed onto a very hot pan sizzles and evaporates very quickly. But if the pan's temperature is well above water's boiling point, "gleaming drops resembling quicksilver" will form and skitter across the surface. It's called the "Leidenfrost effect" in his honor.

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