This Water Drop, It’s the Greatest Dancer

Any water droplet can dance. All it needs is the right dance floor.

Take, for instance, the water drops bouncing around in Yanlin Song’s lab. They twist, twirl and even pirouette after falling onto a special surface he and his colleagues designed.

Dr. Song and his team at the Institute of Chemistry at the Chinese Academy of Sciences study how surfaces interact with water droplets, research that applies everywhere, from your car’s windshield to the wings of an airplane.

To make their surfaces, the researchers covered small alumina plates with a super- water-repellent coating. Then, the team exposed the plates to ultraviolet light, to create water-adhesive designs on top of the coating. When a droplet touched the surface, the water that touched the sticky design rebounded much slower than the water that touched the rest of the water-resistant plate. That difference in speed caused the rebounding droplet to spin.

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Normally when a water droplet hits a plain surface, it immediately recoils straight up. But in this case, the drops bounce right or left, or they spiral, depending on the pattern of the plate. Dr. Song and his team have constructed half-moons, pinwheels and one design that resembles a circle divided into three curved lines. By changing the pattern on the plate, the researchers can essentially control the dancing drop’s choreography.

“The symmetry of the patterns is very important for the behavior of the droplet,” said Dr. Song. “Another factor is the size of the pattern should be comparable with the size of the droplet.”

The team published their results earlier this month in the journal Nature Communications.

Dr. Song recorded some of the drops spinning at about 7,300 revolutions per minute when they bounced back from the special surface. In the future, this technology could be helpful in developing self-cleaning car windshields, defrosting airplane wings or even to harness energy from raindrops, Dr. Song said.

For now, we can just enjoy watching the droplets’ sweet moves.

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