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Tech

We've Been Chasing Super-Hydrophobic Metals Since 1805

Chill out about that water-repelling metal.
Photo by J. Adam Fenster / University of Rochester

Today internet users are in a tizzy about a really off-putting substance. Researchers at the University of Rochester have developed a metal to which water molecules cannot bond. Even when you have a drop of water on a metal surface and it rolls off, it leaves a stream of water behind it; this new substance is so hydrophobic that water literally bounces off it. The potential applications for such a substance are thrilling, but cautious readers know to lower their expectations; this new material isn't very feasible, and it's nowhere near ready to be deployed in those real world scenarios where it's most needed.

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First  theo​rized in 1805, hydrophobic materials have been something of a holy grail for engineers. Though it's not really clear why early engineers might have wanted hydrophobic materials back then, today we've concocted all sorts of uses for them: self-cleaning solar panels, waterless latrines for developing nations, water-proof apparel or medical devices, or surfaces that can't be damaged by rust or ice.

Nature provides a number of materials that don't get wet, including the  lotu​s leaf and the coating on some birds​' feathers, but it turns out this is much harder to do in the lab because of water's physical and chemical properties that draw it to most types of surfaces. But in the 1960s, researchers at DuPont Chemical figu​red out a way to work around water's annoying attractiveness: giving materials a rough surface that doesn't let water molecules bond to it.

Further develop​ment of this theory led researchers to develop "hierarchical structures" that would make materials super-hydrophobic, making them more effective in warding off water's attractive qualities. Today a material is co​nsidered super-hydrophobic if water makes contact with it at a certain angle (150°) and the angle at which a surface needs to be oriented for a drop to roll off it (10°).

University of Rochester researchers developed the most recent super-hydrophobic material using the same principles, according to a st​udy published yesterday in the Journal of Applied Physics. Using a very precise laser, the researchers carved tiny structures into a metal made of platinum, brass and titanium. In addition to being hydrophobic, the resulting material is so dark that it also absorbs light—which the researchers suggest could make it useful in solar panels.

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Does this sound familiar? It should—researchers have been concocting "the next big thing" in hydrophobic materials at an astounding rate. Last year researchers at Brigham Young University created a  spray-o​n material that, combined with etched silicon and a coat of Teflon, would keep water rolling off everything from boots to airplane wings.

Just a few months ago, I  wrote about one that's silicone-based and stable enough to be used in sex toys. In 2013, MIT researchers made a mor​e durable hydrophobic material to be used in power plants that rely on steam. That same year, also at MIT, engineers designed a different type of inter​action between surface structures and water that achieved the same water-shedding result.

But this new material is metal, which might make all the difference, according to Julie Croc​kett, a mechanical engineer at Bringham Young University (she was behind the spray-on material developed there last year). "I would expect these [metal] surfaces to be much more robust than many other currently researched surfaces which, out of necessity, usually include some type of hydrophobic coating, or are fabricated of materials more easily stripped of their structuring," she said via email. "Thus these strong metal surfaces take another step towards overcoming one of the lingering concerns during extensive use of super-hydrophobic surfaces; durability."

Durability is definitely important. But it doesn't look like this material is going to be solving lots of real-world problems anytime soon. "It currently takes an hour to pattern a 1 inch by 1 inch metal sample, and scaling up this process would be necessary before it can be deployed in developing countries," according to the ​pre​ss release.

The Rochester researchers are looking into applying the technique to other materials, which is probably a good idea because developing countries aren't going to have billions of dollars to spend on one of the world's most preciou​s metals for their citizens to literally shit on. And although research​ers don't always know what the application for a material can be until after they have made it, it looks like engraved platinum may not be the solution to the durability issues of hydrophobic materials.

So, buck up; although this material probably won't be put in solar panels and latrines alike all over the world, it's an interesting new entry to a field with limitless applications.