Leidenfrost drops levitate over a hot substrate on a thin layer of their own vapor, constantly replenished as the drop evaporates. For the most part, previous studies have focused on pure droplets, but a new one looks at what happens when you add surfactants – and the results are, well, explosive.
Surfactants are a type of chemical that like to gather at the surface of a drop, and, unlike water, they’re nonvolatile – they don’t evaporate easily. So as the Leidenfrost drop evaporates and shrinks, the surface of the drop becomes more and more crowded with surfactant molecules. Eventually, they form an elastic shell around the remaining water, making evaporation more difficult.
Inside the droplet, the temperature continues to rise, eventually reaching a point where bubbles of vapor can nucleate inside. When that happens, the bubbles expand almost instantaneously and the internal pressure spike bursts the shell, causing the entire droplet to explode. (Image and research credit: F. Moreau et al.)