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IRG-II Nugget

Nanoparticles help see through the fog

Left : a microliter drop of water spreads on the surface of the anti-fogging coating in about 0.16 seconds.   Right : part of a glass slide (bottom three quarters) is coated with the anti-fogging coating. After being cooled and placed in a humid environment, only the top part of the glass (without the anti-fogging coating) becomes fogged. The coated part of the glass slide remains completely clear.

The fogging of car windows, bathroom mirrors, camera lenses, eyeglasses and safety goggles can be a real nuisance or even a life threatening problem. Soldiers in Iraq, for example, are placed in harms way when they are forced to remove their protective eye goggles due to fogging problems. Fogging occurs when microscopic droplets of water condense onto a cool surface and scatter light, which, in turn, drastically impairs light transmission. MIT MRSEC Professors Cohen and Rubner have discovered that thin film coatings comprised of nanoparticles of glass that are about one million times smaller than a grain of sand interact so strongly with water that they force the condensing water droplets to spread out into an ultrathin sheet of water in a fraction of a second (see Figure below). Since a sheet of water does not scatter light, the coating effectively eliminates the fogging problem. These anti-fogging coatings are nanoporous in nature. Since nanopores lower the refractive index of the coating, it also functions as a high performance anti-reflection coating. This new coating has the potential to provide the first "long-lasting" solution to a very common and potentially dangerous problem. The use of nanotechnology to address the commonly observed problem of fogging has resulted in worldwide press coverage including an educational outreach article and companion worksheet on a website entitled "Science News for Kids".

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