NASA released a video on Friday of astronaut Scott Kelly playing ping-pong with a ball of water in space. Kelly did this by forming a ball of water and gently patting it back and forth between two water repellant paddles.
According to the video’s description, Kelly was able to do this because the paddles’ surfaces are superhydrophobic—they repel water.
The paddles are coated with Teflon, the same polymer that makes nonstick pans so easy to clean. Teflon, also known as Polytetrafluoroethylene (or PTFE for short), is a string of carbon atoms surrounded by fluorine atoms. The bonds between the fluorines and carbons are very strong, making the molecule very reluctant to react with and bind to other molecules. In simpler terms, PTFE just likes to hang out by itself and not play with other things, like food, so food doesn’t stick to it. PTFE is also very heat-resistant, making it ideal for cookware, but also for things in space.
But that’s not the only thing making the paddles hydrophobic. PTFE is merely coating the paddles, which are laser-etched to have many tiny nails sticking out from them. This takes advantage of the way liquids, solids, and gases interact when in contact with one another. Liquids will sit on a solid and hold together in a dome due to surface tension. The angle between the solid and the leading edge of the liquid droplet is called the contact angle.
Superhydrophobic surfaces with the little nano-pillars, like the ones Kelly was using, basically make it so the droplet can’t spread out over the surface, widening that contact angle. The liquid will then hold together in something very close to a sphere.
According to Geek.com, the applications of superhydrophobic surfaces include making air conditioning and power plant condensers more efficient. They could also lengthen the lifespan of solar panels and roofs, according to the National Science Foundation.
But we’re thinking water ping-pong is definitely the most fun application. The NASA video is part of a larger series of videos where NASA is using ultra high-definition cameras to do important things like monitor docking and undocking on the International Space Station, but also for fun experiments like watching an Alka-Seltzer dissolve in a water droplet in microgravity.
Hopefully Kelly will continue to regale us with more fun videos as he completes his historic year in space.