Annual Reviews Extra

WATCH: A Water Droplet Pulses Itself Into a 'Star'

17 FEBRUARY 2015

Hi there, I’d like to talk to you about a little something called the Leidenfrost Effect. No, no, don’t leave, I know you vaguely remember hearing about it in high school, but trust me, this is actually super-fascinating stuff. It's how you turn a simple drop of water into something resembling Flubber suffering from a violent heartbeat, or a gently pulsing star.


As Esther Inglis-Arkell writes at io9, the effect works when a fluid makes contact with a surface that’s a whole lot hotter than it is, like when water droplets leak onto a red-hot pan. In the video, you can see the Leidenfrost Effect work its magic as the portion of water that’s directly touching the surface evaporates instantly, and provides a buffer to temporarily protect the water modules above.

Levitating atop the delicate gaseous buffer, the water forms into a bead that zooms around the surface until the vapour disappears and exposes it to the surface heat, causing the droplet to eventually shrink all the way down to nothing.

But what happens if you keep adding more water to the droplet? Well, the droplet will start pulsing and oscillating, and develop into an wobbly oval shape, as you can see above, or a star, like in the video below:

Inglis-Arkell explains at io9:

"The oscillations of the water are driven by the evaporating liquid on the surface below it. The newly-formed vapour will try to make its way upwards any way it can. A ‘chimney' forms within the water droplet, allowing gas to escape but drawing water upwards and drawing the edges of the water inwards. When the chimney closes again, the water collapses back down. When the water forms a shape with three or more ‘points’, it's called a Leidenfrost Star."

And the best thing about this effect is that we can actually control what the water droplet does while enjoying its magic vapour carpet ride. Back in 2013, undergraduate students Carmen Cheng and Matthew Guy from the University of Bath in the UK constructed a Leidenfrost Maze, made from serrated metal surfaces that were heated up and arranged in such a way that the water droplets would travel along a specific path:

Now if only we could figure out how to create entire armies of these very obedient water droplets to do our evil bidding chores for us.

Source: io9