Researchers at Duke University and the University of British Columbia are exploring whether surfaces can shed dirt without being subjected to fragile coatings
Scalpels that never need washing. Airplane wings that de-ice themselves. Windshields that readily repel raindrops. While the appeal of a self-cleaning, hydrophobic surface may be apparent, the extremely fragile nature of the nanostructures that give rise to the water-shedding surfaces greatly limit the durability and use of such objects.
To remedy this, researchers at Duke University in Durham, North Carolina and the University of British Columbia in Vancouver, Canada, are investigating the mechanisms of self-propulsion that occur when two droplets come together, catapulting themselves and any potential contaminants off the surface of interest. They ultimately hope to determine whether superhydrophobicity — a surface that is impossible to wet — is a necessary requirement for self-cleaning surfaces.
“The self-propelled catapulting process is somewhat analogous to pogo jumping,” said Chuan-Hua Chen, an associate professor in the Department of Mechanical Engineering and Materials Science at Duke University. He and his colleagues present their work this week in Applied Physics Letters, from AIP Publishing.
When the droplets coalesce, or come together on a solid particle, they release energy – analogous to the release of biochemical energy of a human body on a pogo stick. The energy is then converted through the interaction between the oscillating liquid drop and the solid particle – analogous to the storage and conversion of energy by the spring mechanism of the pogo stick.
“In both cases, the catapulting is produced by internally generated energy, and the ultimate launching comes from the ground that supports the payload – the solid particle or the pogo stick,” Chen said.