The October 2009 Physics Today cover story looks at the work on superhydrophobic surfaces being done by several researchers in the Mechanical and Industrial Engineering Department. As the story notes, “Researchers led by Jonathan Rothstein at the University of Massachusetts Amherst now offer a proof-of-principle demonstration of a new, passive option for reducing drag in a turbulent flow. They tailored the microscale structure of a hydrophobic material—polydimethylsiloxane (PDMS), akin to the rubbery polymer used to caulk bathtubs—to create air pockets that allow the flow to “slip” (shear free) at the liquid–air interface. The greater the area covered by air pockets, the greater the overall reduction in shear stress—up to 50%, the researchers estimate.”
Besides Rothstein, the other MIE researches cited in the article were Blair Perot, R. J. Daniello, N. E. Waterhouse, J. Ou, and Michael Martell. Link to article.
Turbulent flows of a liquid along a wall, the article explains, experience frictional drag, a macroscopic phenomenon that strongly affects the efficiency, costs, and other parameters of countless engineering systems—from marine vessels to oil pipelines. The drag arises from shear stress, the rate per unit area of momentum transfer from the flow to the wall. To reduce the shear stress, engineers could add polymers to the flow, inject bubbles against the surface, or combine the two methods. But those approaches bear their own costs. (November 2009)