Bursting bubbles break chemical bonds.

Blasting two high-powered jets of liquid into each other is bound to mix things up, and a new study demonstrates just how much. The fast, turbulent flows created by such a collision are powerful enough to break chemical bonds, researchers have found.

The source of this power lies in bubbles, says Kenneth S. Suslick of the University of Illinois at Urbana-Champaign. He and his team used a laboratory device that smashes two fluid jets into each other. The device was originally designed to blend fine droplets of liquid, but Suslick's interest lay in its application to chemistry. He suspected that bubbles rapidly growing and collapsing in the turbulent collision would generate an intense local heating that could drive chemical reactions.

This cavitation process "provides a mechanism for [transforming] mechanical action in a liquid into chemical reaction," Suslick says. He and his colleagues describe their findings in the Oct. 1 Journal of the American Chemical Society.

Cavitation also occurs when ultrasound waves pass through liquids, producing bubbles that grow rapidly and then collapse in a flash of light (SN: 4/29/95, p. 266). In their liquid jet experiments, Suslick's team charted the progress of a standard reaction used in ultrasound chemistry experiments--the formation of triiodide from iodide in a solution of water and carbon tetrachloride.

Fairly high jet pressures are needed, the team found. Below a threshold of about 148 times atmospheric pressure, no reactions occurred.

"I'd be very hard pressed to see how you could do that chemistry unless you had cavitation," says William R. Moser, a chemical engineer at Worcester (Mass) Polytechnic Institute. "I think he's demonstrated something quite important that has general applications." Several years ago, Moser and his coworkers proposed using liquid jets as a way of breaking down chlorine compounds in contaminated groundwater.

Suslick and his group now plan to make the cavitation process more efficient, thus harnessing it for use in chemistry. This approach runs counter to the century-old idea that cavitation is always a problem. Naval engineers have known since the late 1800s that bubbles forming and collapsing on propeller blades make noise and erode the blades. High temperatures and shear forces produced by the bubbles contribute to that deterioration, Moser says.

"It's amusing to go back to it now and see that there are chemical consequences too," Suslick adds.