MIT concocts fogless glass

Fogless windshields may be in your future, if a new technique for coating glass and plastic takes off.

How do you prevent glasses from fogging up? Coat them in water, says a group of researchers at MIT.

At the American Chemical Society meeting in Washington, D.C., this week, scientists from MIT explained how they have developed a new material--which consists of thin, alternating layers of tiny glass particles and polymers--that will resist fogging and work in a far wider range of environments than current fog-resistant glass and plastics. In two to five years, glasses, ski goggles and car windshields could be made with the material. So far, the military (the project was funded by DARPA) and two car manufacturers have expressed interest.

The MIT technique is somewhat counterintuitive since fog develops when tiny water droplets form on a glass surface. The thousands of droplets adhere to a glass or plastic surface at random, sharply angled points. The droplets scatter light in random patterns, causing the surfaces to become foggy to the human eye.

Rather than repel water, the new coating attracts it. The water then forms a thin, continuous layer across the surface, reducing the scattering of light without creating distortion. The same principle is at work when you can suddenly see through a foggy scuba mask once under water.

The thin layer of water also helps reduce glare. So far, the coating is more durable on glass than plastic surfaces, but project leader Michael Rubner, a materials science researcher at the university, and his associates are currently working on processes to optimize the effectiveness of the coating for all surfaces.

As an added bonus, the material potentially will be cheap to manufacture. It consists of layers of silica nanoparticles, which are basically tiny particles of glass, and a polymer called polyallylamine hydrochloride.

Currently, anti-fog technology largely consists of spray-on coatings, which wear off over time, or titanium dioxide particles, which work only in some environments.

Glass, plastics and other basic industrial materials are--and likely will be--the first products enhanced by nanotechnology. Technically, nanotechnology refers to the science of building products out of components measuring less than 100 nanometers, or 100 billionths of a meter. In practical terms, it involves trying to get every atom in a material to do its job. This can come in the form of reduced weight or new properties.

At Ohio State, for instance, professor Bharat Bhushan is adding bumps to glass in a way that makes surfaces repel water. The design is based around the similar principles behind lotus leaves. Meanwhile, Aspen Aerogels has come up with insulation that, at 1/4 inch thick, will potentially replace fiberglass insulation.

Waterproof paper was also recently devised by Ecology Coatings.

Other papers that will be released at the convention include one on techniques to prevent the spread of invasive plants such as the kudzu, a Eurasian plant that has wreaked havoc in the Eastern United States.

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