Newswise — Foggy
windows and lenses are a nuisance, and in the case
of automobile windows, can pose a driving hazard.
Now, a group of scientists at the Massachusetts Institute
of Technology (MIT) 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.
transparent coating can be applied to eyeglasses,
camera lenses, ski goggles … even bathroom mirrors,
they say. The new coating was described today at
the 230th national meeting of the American Chemical
Society, the world's largest scientific 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
“Our coatings have the potential to provide the
first permanent solution to the fogging problem,” says
study leader Michael Rubner, Ph.D., a materials science
researcher at MIT in Cambridge, Mass. “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, he says.
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.
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,” Rubner says.
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, the researcher says. So far, the coating is more durable on glass than
plastic surfaces, but Rubner and his associates are currently working on processes
to optimize the effectiveness of the coating for all surfaces. More testing
is needed, they say.
Funding for this study was provided by the Defense
Advanced Research Projects Agency (DARPA) and the
National Science Foundation (via the Materials Research
Science and Engineering Centers, or MSREC).
The American Chemical Society is a nonprofit organization,
chartered by the U.S. Congress, with a multidisciplinary
membership of more than 158,000 chemists and chemical
engineers. It publishes numerous scientific journals
and databases, convenes major research conferences
and provides educational, science policy and career
programs in chemistry. Its main offices are in Washington,
D.C., and Columbus, Ohio.
paper on this research, PMSE 92, will be presented
at 8:00 a.m., Monday, Aug. 29, at the Grand Hyatt
Washington, Franklin Square room, during the symposium “Assembly
of Polymers and Nanoparticles – From 2-D to 3-D.”
Michael F. Rubner, Ph.D., is a materials scientist at the Massachusetts Institute
of Technology in Cambridge, Mass.