Research team is first to identify surface ‘roughness’
required to achieve amazing feat
(August 19, 2015) 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 theoretical mechanical engineer 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.