Anti-fog Glass

Anti-Fog Glass

Car windows, eyeglasses, camera lenses, even our bathroom mirrors are all victims of the frustrating effects of fogging. But scientists at MIT might finally have a solution. This ScienCentral News video has more.

I Can See Clearly Now…

It's a ritual we go through every winter — start up the car, turn on the defogger, and… wait. Now, researchers at the Massachusetts Institute of Technology think they have a "clear" solution for permanently unfogging our view.

"Basically you would never have that problem, you wouldn't have to wait for the car to warm up because no fog would be formed on any of the inside windshields," explains materials scientist Michael Rubner.

We've all been driven half crazy by a windscreen or a pair of glasses that keep fogging up. More than just a nuisance, fogging can pose a driving hazard. Glass fogs up when warm, moist air comes into contact with glass and cools so that thousands of tiny water droplets form on the glass. The droplets scatter light, making oncoming traffic hard to see.

And it's not just a problem in our cars. Fogging is an annoying problem for anyone who wears glasses, likes to take pictures or goes skiing or scuba diving.

As reported in Discover magazine, Rubner and his research team turned to nanotechnology and recently announced the development of a permanent glass coating that keeps fog at bay.

Their superhydrophillic — water loving — coating is composed of nanoparticles made of silica, the same material that glass is made from, to create a coating with a rough surface, although it looks smooth to the naked eye.

"We've figured out a way to assemble these very tiny particles of glass onto a surface using polymer chains," explains Rubner. "A polymer chain is a long chain-like molecule and in this case the process we've developed the polymer chain has a positive charge, whereas the glass particles have a negative charge, so we use a positive to negative attractive force to build these layers up onto the surface. The net result is we create a very porous coating, that is, a coating that has lots of holes in it. "

The silica particles form layers of tiny pores, each a thousand times smaller than the width of a human hair. The pores attract the tiny droplets of water that make up the foggy surface. Stacked ten to twenty layers thick, with air pockets in between, these pores create what's called a "wicking" effect, which forms the water droplets into a uniform sheet."When you put a droplet on that surface, the water is drawn into these pores instantaneously and wicked away into a uniform sheet," he says. "The net result is we don't create water droplets on the surface that can scatter light, and we have a nice transparent lens in this case."

He says his cheaply produced technology has the added benefit of increasing the clarity of unfogged glass. It reduces the glare and allows more than 99 percent of light to pass through the glass, compared to untreated glass that scatters between four and eight percent of light.

"Because we're building a thin film coating that is filled with holes, it means that the coating also acts as an anti-reflection coating. That is, it will allow more light to pass through, for example, your glass windshield or your camera lens," Rubner says.

Most current solutions don't work: anti-fogging sprays are short-lived; and windshields coated with titanium dioxide require exposure at least every few hours to ultraviolet light to work.

"It's very difficult to prevent fogging from taking place. That is it's very difficult to prevent the condensation of water droplets onto the surface, so what most technologies try to do is to create a surface that loves water so much that when the water hits the surface it spreads out into a uniform thin film on the surface," he says. "So existing technologies for example put different types of materials onto that lens that promote this spreading of water using materials that really like water, in fact in some cases the very same materials that are used in diapers are used on the surfaces of lenses, for example, because they love to draw water and spread it out across the surface.

Rubner is not the only one to come up with this clever idea, an Australian company called Xerocoat is also trying to develop and anti-fog coating. Rubner isn't currently associated with any particular company, but he hopes to have his technology on the market in the next few years… giving us one less thing to do on cold mornings and a little more safety on the winter roads.

Rubner's work was presented at the August, 2005, Meeting of the American Chemical Society, and was funded by the National Science Foundation as part of the Materials Research Science and Engineering Centers, and the Department of Defense via the Defense Advanced Research Projects Agency (DARPA).

"Basically you would never have that problem, you wouldn't have to wait for the car to warm up because no fog would be formed on any of the inside windshields," explains materials scientist Michael Rubner.

Looks like the teenagers having sex in their cars will have to get window shades now. . . No more fog so people can't see in :laugh: