Anti-Fog Coating May Be First to Be Permanent

Imagine a day when your car windshield will never fog up — and when your eyeglasses never get all annoyingly misty. An MIT researcher has developed what he claims is the first permanent fog-resistant coating. The world already has anti-fog sprays, but they must be reapplied over time. At least two major car manufacturers have already expressed interest, he says.

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ROBERT SIEGEL, host:

This is ALL THINGS CONSIDERED from NPR News. I'm Robert Siegel.

MELISSA BLOCK, host:

And I'm Melissa Block.

It's annoying when your car windshield fogs up or when your eyeglasses get all misty. There are anti-fogging sprays, but they don't last forever. Now scientists say they've made a truly permanent anti-fog coating that's as durable as glass itself; that's because the coating is made of glass. NPR's Nell Boyce ventured into a steamy bathroom to see how well it works.

NELL BOYCE reporting:

Michael Rubner works at the Massachusetts Institute of Technology. He's come to Washington, DC, to show off his new anti-fog coating at a meeting of the American Chemical Society. So we can see it in action, we go into his hotel bathroom...

(Soundbite of water)

BOYCE: ...turn on all of the hot-water faucets and wait for the fog to rise.

(Soundbite of water)

Mr. MICHAEL RUBNER (Massachusetts Institute of Technology): Fog is a process where very, very small droplets of water condense on the surface, and they're small enough that they can scatter light. So when they scatter light, it makes it very difficult for you to see through that piece of glass.

BOYCE: What anti-fog coatings do is make a surface more water-loving. They make water droplets spread out into a thin, see-through film.

Mr. RUBNER: The water is still there, but since it's a uniform sheet, it can't scatter light, so it remains transparent.

BOYCE: Rubner says there are already anti-fog technologies out there, but all have drawbacks. They need to be reapplied, or they only work under certain conditions. To make his coating, Rubner relies on incredibly small pieces of glass. They're far more miniscule than dust. He glues the particles onto a sheet of glass using sticky molecules of plastic. If you look through a powerful microscope, the new coating looks a lot like a sponge.

Mr. RUBNER: And it's that porous structure that helps to draw water in, so when you put a drop of water on there, it's immediately wicked into the porous structure and drawn into the glass coating. And that's how you get that nice sheeting like that.

(Soundbite of water being shut off)

BOYCE: So does it work in a steamy bathroom? Rubner holds up a small rectangle of ordinary glass. Half is covered with his coating. We peer through it at each other.

It's like a rain forest in here.

Mr. RUBNER: Mm-hmm, yeah. So the other side is remaining very clear and transparent, whereas the side that doesn't have the coating has a whole bunch of moisture and fog collected on it and difficult to see through.

BOYCE: To make the coated glass tough enough for a windshield or a pair of eyeglasses, Rubner heats it to over a thousand degrees Fahrenheit. The plastic glue burns away. The bits of glass fuse into a solid sponge.

Mr. RUBNER: We get exactly the same properties, but we have a beautifully durable coating now, very much like glass would be regularly.

BOYCE: Rubner's still working on how to coat plastics, which can't take the heat. For glass, he says the process should be relatively cheap and easy. Some companies, like carmakers, are interested. But perfecting fog-free glass could take years. Until then, you'll just have to wipe off mist the old-fashioned way.

(Soundbite of water being shut off)

BOYCE: Nell Boyce, NPR News.

(Soundbite of drips of water)

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