Physics & Math

Alberto Tufaile, a physicist at the University of São Paulo in Brazil, was studying bubble formation in a chamber of glycerol when he noticed something peculiar. "Suddenly, we started seeing strange bubbles that didn't rise and lasted an hour or more if they didn't touch bottom. We didn't know what they were," he says. He and his colleague, physicist Jose Carlos Sartorelli, found a partial answer on a Web site created by amateur bubblemakers. The mystery blobs were anti-bubbles, spheres of liquid suspended inside a shell of air. Intrigued, Tufaile and Sartorelli set out to make the first scientific study of these little-understood objects.

An anti-bubble (above) takes shape when one rising bubble collides with another, researchers found. "The second one can get captured by the first, forming a tiny droplet surrounded by a skin of air," Tufaile says. Such captures occur most frequently when air flows into the glycerol with just enough force to create bubbles without stirring up turbulent ripples. An improved understanding of anti-bubbles might prove useful. "Anytime you see a big tower at an industrial plant, there is a bubbling process going on. Depending on the process, anti-bubbles could cause problems, or they could enhance the efficiency of the reaction," Tufaile says.