Liquid Ping Pong in Space
NASA astronaut Scott Kelly, who marked day 300 of a historic year in space on Jan. 21, 2016, shows off another fascinating feature of life in microgravity. Kelly used two paddles with hydrophobic, or water repellant, features to pass a sphere of water back and forth. Scientists use the microgravity environment of the space station to advance scientific knowledge in Earth, space, physical, and biological sciences that otherwise wouldn’t be possible down here on the planet.
The paddles are polycarbonate laser etched so that the surfaces are actually arrays of 300 micrometer posts (0.3mm). The surfaces were then spray coated with a Teflon coat. The combined effects of surface roughness and non-wettability produce a super-hydrophobic surface capable of preventing water adhesion in dynamic processes. The larger the drop, the less force it takes to break it up. The smaller the drop, the harder you can hit it. Scott is demonstrating about a 4 mL drop (over 100 times larger than a rain drop).