Raindrops keep falling on my head
In heavy rain, raindrops can hurt. But imagine that you are an insect, or the leaf of a plant—those raindrops at terminal velocity are like bullets hitting your surface. Why are small things not damaged?
It turns out that such biological surfaces have a structure at the microscopic scale that is hydrophobic (water repelling). Researchers found that the rain drops just bounce off such surfaces. How?
The droplets spread as they hit what looks like a rough surface, covered in micro-bumps. A shock-wave forms, creating tiny holes in the upper surface of the droplet. Then the holes join up, the droplet shatters and rebounds off the leaf or insect. This reduces the contact time by 70%.
Clever design!
- Kim, S., et al. How a raindrop gets shattered on biological surfaces, PNAS 117(25):13901–13907, 23 Jun 2020.
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