BU Assistant Professor James C. Bird (ME, MSE) and collaborators in the Varanasi group at MIT's [...]Department of Mechanical Engineering found that when they augmented micro- or nanostructured surfaces with periodic, wrinkle-like features, liquid drops bounced off at faster rates than previously thought possible. The engineers reported their findings in the cover story of the November 21 issue of Nature.
In the top video, prior to adding ridge-like features to a micro- or nanostructured surface, a water drop would spread out to a maximum diameter, retract until the edges of the drop met its stationary center point, and bounce off the surface. With the introduction of the ridges (bottom video), the center point moved to meet the edges as the drop recoiled, heading it off at the pass. The drop then split in two before jumping off the surface.
"We've demonstrated that we can use surface texture to reshape a drop as it recoils in such a way that the overall contact time is significantly reduced," said Bird, the paper's lead author, who directs the Interfacial Fluid Dynamics Laboratory at BU. "The upshot is that the surface stays drier longer if this contact time is reduced, which has the potential to be useful for a variety of applications."
Such surfaces may improve the performance of systems that operate better under dry conditions, such as steam turbines or aircraft wings, and enable cold surfaces, such as rooftops, to resist icing by shedding liquid drops before the drops freeze.