December 12, 2005 Nanotachnology looks set to permanently fix the problem of fogging glass, with the news that a team of MIT scientists has developed a silica nanoparticle polymer coating for glass or plastic that creates a permanent non-fog surface. When commercialized sometime in the next few years, the technology will find immediate application in products such as eyeglasses, helmet visors, camera lenses, skiing goggles, bathroom mirrors and shower screens, but it will be in our cars that we will most likely first encounter the technology. Driving is a sight-response game and if you can’t see, you’ll lose. Not surprisingly, the Defense Advanced Research Projects Agency (DARPA) was one of the major funders of the project as having a foggy windscreen makes you vulnerable in battle as well as on the roads. When a cold surface suddenly comes into contact with warm, moist air, thousands of tiny water droplets condense on it, scattering light in random patterns and causing the surface to become translucent. The coating prevents this by attracting the water droplets and reducing their contact angles with the surface. As a result, the droplets merge into a uniform, transparent sheet rather than forming countless individual light-scattering spheres. Nanotechnology will also enable the same coatings to have superior anti-reflective properties that reduce glare and maximize the amount of light passing through (good for greenhouses and solar cell panels).
Anti-fog technology has been offered before as an anti-fog spray which needs to be regularly applied to remain effective – the MIT solution is permanent.
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"Our coatings have the potential to provide the first permanent solution to the fogging problem," says co-study leader Michael Rubner, the TDK Professor of Materials Science and Engineering. "They remain stable over long periods, don't require light to be activated and can be applied to virtually any surface." Coated glass appears clearer and allows more light to pass through than untreated glass while maintaining the same smooth texture, said Rubner, who collaborated on the work with Robert Cohen, the Raymond A. and Helen E. St Laurent Professor of Chemical Engineering.
The coatings consist of alternating layers of silica nanoparticles, which are basically tiny particles of glass, and a polymer called polyallylamine hydrochloride, both of which are relatively cheap to manufacture, Rubner says. He has applied for a patent on the manufacturing process and says that the coating could be available in consumer products in two to five years. The military and at least two major car manufacturers have already expressed interest in using the technology, he says.
When fogging occurs, thousands of tiny water droplets condense on glass and other surfaces. The droplets scatter light in random patterns, causing the surfaces to become translucent or foggy. This often occurs when a cold surface suddenly comes into contact with warm, moist air.
The new coating prevents this process from occurring, primarily through its super-hydrophilic, or water-loving, nature, Rubner says. The nanoparticles in the coating strongly attract the water droplets and force them to form much smaller contact angles with the surface. As a result, the droplets flatten and merge into a uniform, transparent sheet rather than forming countless individual light-scattering spheres. "The coating basically causes water that hits the surfaces to develop a sustained sheeting effect, and that prevents fogging," says Rubner, who is director of MIT's Center for Materials Science and Engineering.
The same coatings also can be engineered to have superior anti-reflective properties that reduce glare and maximize the amount of light passing through, an effect that shows promise for improving materials used in greenhouses and solar cell panels. So far, the coating is more durable on glass than plastic surfaces, but Rubner and colleagues are currently working on processes to optimize the effectiveness of the coating for all surfaces.
This work was funded by the Defense Advanced Research Projects Agency (DARPA) and the National Science Foundation.