>"While we fabricated several different nanotextures that all significantly increased the water repellency, certain shapes performed differently than others," said Brookhaven physicist and co-author Atikur Rahman. The enhanced water-repellency was consistent with earlier studies, including a previous one by Checco and collaborators that showed that air bubbles trapped in the textured surfaces force the water to ball up into drops
. However, in the current study, the team further showed that cone-shaped nanostructures are significantly better than cylindrical pillars at forcing water droplets to roll off the surface, thus keeping surfaces dry.
"In the case of the cylindrical pillars, as the contact line of the droplet recedes on the textured surface, it can get pinned to the nanotexture, leaving behind a microscopic liquid layer on the pillars' flat tops instead of a perfectly dry substrate," Checco said. "The cone-shaped structures have smaller, pointed tops, likely preventing this effect."
The other important finding was that the water-repelling ability of cone-shaped nanotexturing held up even when water droplets were sprayed onto the surface with a pressurizing syringe. Such pressure could potentially force water into the nanosized pockmarks between the conical or cylindrical pillars, displacing the air bubbles and destroying the water-repelling effect.
The scientists monitored the splashing droplets using a high-speed camera capable of capturing 30,000 frames per second. For the cone-textured surface, "The sprayed droplets splash and eject satellite droplets that spread radially outward while the centermost portion of the original drop flattens out, then recoils, and bounces off the surface," Checco said. "We do not observe any pinned drops at the impact point after the drop has bounced back, indicating that the surface remains water-repellent during the impact Page: 1 2 3 4 Related biology technology :1
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