MIT research could clear up foggy problem
MIT research could clear up foggy problem
http://web.mit.edu/newsoffice/2005/fog.html
Foggy windows and lenses are a nuisance, and in the case of
automobile windows, can pose a driving hazard. Now, MIT scientists
may have found a permanent solution to the problem. The team has
developed a unique polymer coating--made of silica
nanoparticles--that they say can create surfaces that never fog.
The transparent coating can be applied to eyeglasses, camera lenses,
ski goggles ... even bathroom mirrors, they say. The
new coating was described Aug. 29 at the national meeting of the
American Chemical Society.
Researchers have been developing anti-fog technology for years, but
each approach has its drawbacks. Some stores carry special anti-fog
sprays that help reduce fogging on the inside of car windows, but the
sprays must be constantly reapplied to remain effective. Glass
containing titanium dioxide also shows promise for reduced fogging,
but the method only works in the presence of ultraviolet (UV) light,
researchers say.
"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.
.
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