A series of images show two water drops coalescing on a polystyrene particle. As they catapult back up, the merged droplet carries the particle away from the supporting substrate. Photo by Roger L. Chavez/Duke University
RALEIGH, N.C., July 5 (UPI) -- Often, the nanostructures that give materials their self-cleaning properties -- or that help surfaces shed water and prevent icing -- also undermine the materials' stability and durability.
A team of researchers from Duke University and the University of British Columbia have found a workaround to the problem, designing self-cleaning material systems that use bouncing water droplets to remain free of contaminants -- but without the added fragility of superhydrophobic coatings.
Superhydrophobicity is the quality of being extremely difficult to wet. A superhydrophobic surface repels water and other fluids with incredible efficiency. Originally, researchers though superhydrophobicity was a necessity for a phenomenon whereby water droplets coalesce and self propel themselves from the surface of a material.
A closer look at droplet coalescence showed superhydrophobic surfaces aren't a necessity.
When two droplets converge on a material, the energy transfer between droplets and surface results in a pogo stick-like oscillation. Researchers showed this energy can be harnessed to carry away contaminant particles.
"The solution suddenly occurred to us while we were examining the drop coalescence process with numerical simulations by my student Fangjie Liu," Chuan-Hua Chen, an associate professor of mechanical engineering and materials science at Duke, explained in a news release. "The coalescence of two droplets on a particle can provide the source of energy to catapult the particle, much like pogo jumping."
In lab experiments, researchers found as the droplets coalesce, the merged droplet can carry away a solid particle resting on a substrate as it catapults back off the surface.
"Since neither the solid particle nor the supporting substrate are superhydrophobic, we clearly demonstrated the feasibility of coalescence-induced self-cleaning without resorting to superhydrophobic surfaces," Chen concluded.
The new research is detailed in a new paper, published this week in the journal Applied Physics Letters.
