Water droplets spontaneously bounce, sans trampoline

water droplets

TRAMPOLINING H2O  A water droplet initially at rest bounces higher and higher in this time-sequence image.

T. M. Schutzius, G. Graeber, D. Poulikakos

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When in a tough spot, some water droplets bounce their way to freedom.

Initially stationary droplets on an extremely water-repellent surface such as etched aluminum bounce as if on a trampoline, researchers at ETH Zurich reveal in the Nov. 5 Nature. The scientists suspect that speedy molecules of water vapor stuck between the droplet and the surface exert enough pressure to launch the droplet skyward.

The phenomenon occurs only if the surrounding air pressure is about a hundredth of that at sea level. Still, studying the interaction of water with various materials could lead to better water-repellent and deicing surfaces. 

BOUNCE POWER This water droplet is put to work. Its spontaneous bouncing on an extremely water-repellent (superhydrophobic) surface drives the motion of a cantilever beam. T. M. Schutzius, D. Poulikakos

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