Burning droplets bounce again. Credit score: Zulu et al., 2025
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 may be additionally an inverse Leidenfrost impact, first described in 1969, that entails a scorching object equivalent to a droplet levitating above a chilly floor. Understanding the mechanisms behind these phenomena is essential to a broad vary of sensible purposes, equivalent to self-cleaning, anti-icing, anti-fogging, floor cost printing, or droplet-based logic techniques.
Droplets often solely bounce if the floor is superheated or engineered ultimately to scale back stickiness. Physicists from the Metropolis College of Hong Kong have found out methods to obtain this bouncing conduct of scorching oil droplets off virtually any floor, in accordance with a new paper printed within the journal Newton.
As we have reported beforehand, in 1756, a German scientist named Johann Gottlob Leidenfrost reported his statement of the weird phenomenon. Usually, he famous, water splashed onto a highly regarded pan sizzles and evaporates in a short time. But when the pan’s temperature is effectively above water’s boiling level, “gleaming drops resembling quicksilver” will kind and skitter throughout the floor. It is known as the “Leidenfrost impact” in his honor.
Within the ensuing 250 years, physicists got here up with a viable rationalization for why this happens. If the floor is not less than 400° Fahrenheit (effectively above the boiling level of water), cushions of water vapor, or steam, kind beneath them, maintaining them levitated. The Leidenfrost impact additionally works with different liquids, together with oils and alcohol, however the temperature at which it manifests can be completely different.
The phenomenon continues to fascinate physicists. As an illustration, in 2018, French physicists found that the drops aren’t simply driving alongside on a cushion of steam; so long as they aren’t too huge, in addition they propel themselves. In 2019, a global crew of scientists lastly recognized the supply of the accompanying cracking sound Leidenfrost reported. The scientists discovered that it is dependent upon the scale 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.
