High-speed cameras and UV-sensitive materials are helping advance understanding of bubbles — which could mean big things for nanoparticles. In fact, a system in which bubbles mix liquids is an energy-efficient route toward producing nanoparticles. A team from Princeton University has demonstrated that some of the tiny particles that are hurled when a bubble pops can actually be pushed down into the water when that water is covered with oil. Previously, such particles, which are produced by bursting bubbles’ aerosol droplets, have typically only been known to launch outward. The results of the new study offer new insight into the mixture of nonsoluble liquids, the researchers said. The researchers send bubbles through a tank containing a thin surface of oil above water. Images courtesy of Frank Wojciechowski/Princeton University Office of Engineering Communications. The high-speed camera helped break down all steps involved in a bubble’s final pop, finding that each bubble’s collapse caused a pressure wave that pushed a small amount of liquid out and away from the collapsing void. “If you look at this system, which has a thin layer of oil over water, the bursting bubbles were dispersing the oil phase in the form of nanodroplets into the water,” said researcher Jie Feng, a doctoral candidate at Princeton. “Essentially, it is an unrealized form of mass transport related to bubble bursting.” Additional tests were conducted specifically on the nanodroplets and their activity in the water. In one such experiment, the researchers spread a very thin layer of latex particles over the water and were able to observe them as they moved into the water. A layer of material that is sensitive to UV light was then added — the researchers used that light to solidify the droplets, allowing further observation in the water mixture. Princeton University researchers observe the bubbles in a tank. They found that water in one of the test containers changed from clear to translucent after bubbles ran through the mixture for some time. Such change in the appearance “suggested that small objects had been dispersed in the lower water phase,” they said. The addition of a surfactant (which decreases surface tension) became critical in the formation of the nanodroplets, according to the researchers, noting that these droplets did not form without a proper amount of the surfactant. “This system offers an energy-efficient route to produce nanoparticles, with the potential to increase in scale, for applications in a variety of fields such as drug delivery, food production and materials science,” Feng said. The work was funded in part by the Consortium for the Molecular Engineering of Dispersant Systems, the BP/Gulf of Mexico Research Initiative and the European Union's Beyond Everest project. The research was published in Nature Physics (doi: 10.1038/nphys3003). For more information, visit www.princeton.edu.