Bouncing water droplets can get higher with every hop—weird enough for you? In fact, researchers have made it happen for the first time, and today in Nature they describe the strange phenomenon, called trampolining. It requires two ingredients: low air pressure and a “superhydrophobic” surface that fiercely repels water. This surface is composed of tiny pillars and treated with a water-repellant coating. When the scientists put a droplet of water on the surface, the pillars support the water and create a layer of air between the droplet and the surface—like a ball resting on a bed of nails. As the water naturally evaporates, the vapor fills the area in between the pillars below the droplet, building pressure. Result: The droplet spontaneously leaps into action—gaining airtime with every bound, just as a gymnast would on a trampoline. At higher pressure, the droplets can perform a different trick, called “ice levitation.” Evaporation cools the water until it freezes, and a droplet’s vapor kicks it off of the surface as it solidifies into ice. After launch, the frozen pellet lands back on the ground, dead in its tracks. The researchers hope similar surfaces could help make winter roads less icy and kitchen countertops easier to clean.
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