Imagine staying dry underwater for months. Now Northwestern University engineers have examined a wide variety of surfaces that can do just that — and, better yet, they know why. The research team is the first to identify the ideal “roughness” needed in the texture of a surface to keep it dry for a long period of time when submerged in water. The valleys in the surface roughness typically need to be less than one micron in width, the researchers found. That’s really small — less than one millionth of a meter — but these nanoscopic valleys have macroscopic impact. Understanding how the surfaces deflect water so well means the valuable feature could be reproduced in other materials on a mass scale, potentially saving billions of dollars in a variety of industries, from antifouling surfaces for shipping to pipe coatings resulting in lower drag. That’s science and engineering, not serendipity, at work for the benefit of the economy.
“The trick is to use rough surfaces of the right chemistry and size to promote vapor formation, which we can use to our advantage,” said Neelesh A. Patankar, a professor of mechanical engineering in the McCormick School of Engineering and Applied Science, who led the research. “When the valleys are less than one micron wide, pockets of water vapor or gas accumulate in them by underwater evaporation or effervescence, just like a drop of water evaporates without having to boil it. These gas pockets deflect water, keeping the surface dry,” he said.