Using a Rough Surface to Stay Dry
*Researchers at the Massachusetts Institute of Technology and Boston University have found a new clue to staying dry, and it has to do with time and texture.
James C. Bird, now of Boston University, and Kripa K. Varanasi at M.I.T. and their colleagues, were considering the problem of icing, which is a version of getting wet, and they decided to focus on the time a water drop stays in contact with a surface.
There is a maximum amount of time a water drop can touch frozen material before it freezes and sticks, causing all sorts of problems for wings and machinery, for starters.
They tested ways to shorten the amount of contact time, and recorded the tests with high-speed video, which they analysed. A smooth surface might seem most likely to repel water, but they found that a rough surface, with ridges, for example, worked better.
The key is the way a water drop changes shape and bounces off material that has been treated to make it super water-repellent. The drop flattens into a pancake, then recollects itself and bounces up.
Ridges broke up the drops, and the smaller droplets re-formed and bounced away up to 40 percent quicker than the larger drops.
With refinements, Dr. Varanasi said they hope to be able to cut the contact time by 80 percent. If it can then be adapted for industrial uses, it could benefit wind turbines, other kinds of machines, and even the fashion industry.
After their discovery, the scientist looked to nature to see if plants and animals had evolved the same trick. And they had. Although the lotus leaf is often thought of as highly water-repellent, nasturtiums did better, with a rougher surface. They also found the wings of the Morpho Butterfly bounce water off in the same way.
While we like to stay afloat (harf harf) of all topics water, we are in no way suggesting that you use your water cooler as a test site for anything. Yes, that will include water spray ratio, rough surfaces; how high water will bounce off the carpet vs. the floorboards – none of it. We ask, as I’m sure your company does, that you use the water cooler for its primary purpose – supplying you with cool, fresh drinking water at the press of a button.
*Excerpts from an article in the New York Times by James Gorman