Droplets bouncing off surfaces are an on a regular basis phenomenon, like raindrops bouncing off lotus leaves or water drops scorching in a scorching pan, levitating and sliding round—aka the Leidenfrost impact. There’s additionally an inverse Leidenfrost impact, first described in 1969, that includes a scorching object reminiscent of a droplet levitating above a chilly floor. Understanding the mechanisms behind these phenomena is essential to a broad vary of sensible functions, reminiscent of self-cleaning, anti-icing, anti-fogging, floor cost printing, or droplet-based logic programs.

Droplets often solely bounce if the floor is superheated or engineered not directly to scale back stickiness. Physicists from the Metropolis College of Hong Kong have discovered learn how to obtain this bouncing habits of scorching oil droplets off nearly any floor, in accordance with a new paper revealed within the journal Newton.

As we have reported previously, in 1756, a German scientist named Johann Gottlob Leidenfrost reported his observation of the bizarre phenomenon. Usually, he famous, water splashed onto a very popular pan sizzles and evaporates in a short time. But when the pan’s temperature is nicely above water’s boiling level, “gleaming drops resembling quicksilver” will type and skitter throughout the floor. It is referred to as the “Leidenfrost effect” in his honor.

Within the ensuing 250 years, physicists got here up with a viable rationalization for why this happens. If the floor is a minimum of 400° Fahrenheit (nicely above the boiling level of water), cushions of water vapor, or steam, type beneath them, preserving them levitated. The Leidenfrost impact additionally works with different liquids, together with oils and alcohol, however the temperature at which it manifests might be completely different.

The phenomenon continues to fascinate physicists. As an illustration, in 2018, French physicists discovered that the drops aren’t simply using alongside on a cushion of steam; so long as they aren’t too massive, additionally they propel themselves. In 2019, a world staff of scientists finally identified the source of the accompanying cracking sound Leidenfrost reported. The scientists found that it relies on the dimensions of the droplet; it is the bigger drops that explode with that telltale crack. You may even obtain the Leidenfrost impact with ice, as physicists at Virginia Tech demonstrated in 2022.