To the human eye, the burst of a soap bubble appears complete and instantaneous, but high-speed video reveals the directionality of the process. Surface tension is responsible for the spherical shape of the bubble, and, when the bubble is pierced, surface tension is broken, causing the soap film that was the bubble to contract like elastic that’s been stretched and released. Droplets of liquid fly out from the edges of the sheet until it atomizes completely.
Tag: droplet ejection
Breaking Water with Sound
Previously we saw how vibration could atomize a water droplet, breaking it into a spray of finer droplets. Here astronaut Don Pettit shows us what the process looks like in microgravity using some speakers and large water droplets. At low frequencies the water displays large wavelength capillary waves and vertical vibrations. Higher frequencies–like the earthbound experiment on much smaller droplets–cause fine droplets to eject from the main drop when surface tension can no longer overcome their kinetic energy. (submitted by aggieastronaut, jshoer and Jason C)
(Source: /)Vibrating Oil
This high-speed video shows the behavior of oil on a vibrating surface. As the amplitude of the vibration is altered various behaviors can be observed. Initially small waves appear on the surface of the oil, then the surface erupts into a mass of jets and ejected droplets, reminiscent of a vibrated interfaces within a prism or vibration-induced atomization. When the amplitude is reduced after about half a minute, we see Faraday waves across the surface, as well as tiny droplets that bounce and skitter across the surface. They are kept from coalescing by a thin layer of air trapped between the droplet and the oil pool below. Because of the vibration, the air layer is continuously refreshed, keeping the droplet aloft until its kinetic energy is large enough that it impacts the surface of the oil and gets swallowed up.
Jumping Water Droplets
Superhydrophobic surfaces resist wetting from water, but it turns out they can also trigger interesting behaviors in the tiny droplets condensing on the surface. High-speed video reveals that when two condensate droplets coalesce, the energy released by surface tension causes the new droplet to jump off the surface. The phenomenon is the same as one observed in some types of mushroom–when a condensate droplet touches a wetted spore, the spore is ejected from the mushroom. (Video credit: J. Boreyko)
Ejecting Drops
Large droplets ejected from a liquid pool do not coalesce immediately back into the whole. Instead, a thin layer of air gets trapped beneath them, much like the oil lubricating bearings. The weight of the droplet causes the air to drain away, and eventually the droplet comes in contact with the pool. Some of the droplet gets drained away before surface tension snaps the interface back into a low energy state. A new smaller droplet then bounces upward before repeating the process over again. Eventually the droplet becomes small enough that its entire mass gets sucked away by the pool. Researchers call this process the coalescence cascade.