New Nanotech Coating Prevents Fogging, Glare in Glass

Ben Harder
for National Geographic News

August 29, 2005

A new technique for treating glass can permanently prevent glass from fogging and virtually eliminate glare, scientists reported today.

The treatment could improve everything from car windshields and eyeglasses to camera lenses and solar panels, according to the leader of a research group at the Massachusetts Institute of Technology.

MIT materials scientist Michael Rubner presented his team's findings this morning at a chemistry conference in Washington, D.C.

Unlike other anti-fogging coatings, the new technology doesn't have to be reapplied or exposed to light in order to work, Rubner said. Both simple and inexpensive, the new fog-resistant treatment could be conveniently mass-produced, he added.

"It's a cheap, simple process," Rubner said. "I could teach you how to do this, and you could make these [products] in your garage."

The Science of Fog

Fogging occurs when warm, moist air comes in contact with glass and cools, depositing microscopic water droplets. The droplets form "little islands on the surface that are just the right size to scatter light," Rubner said.

Some existing coatings can prevent these droplets from forming. A thin layer of titanium oxide, for example, spreads water into sheets that don't scatter light.

But titanium oxide only works when it has been exposed to specific wavelengths of radiation, such as ultraviolet light. Consequently, titanium oxide-treated glass often fogs up at night or when it has been kept in a darkened storage area.

To make the new coating, Rubner and his collaborators dissolved charged molecules called polymers in one beaker of water and mixed microscopic spheres of glass with the opposite charge into another.

"All we do is dip the [glass surface] into solution A, rinse it a little bit, and dip it into solution B," Rubner said. That creates alternating layers of polymers and glass nano-particles.

"Usually, it takes between 10 and 20 layers to get the desired coating," which is about a hundred nanometers—or a hundred-thousandth of a centimeter—thick, Rubner said.

The many layers form a porous stack that absorbs water before it can form droplets on the surface.

By pulling droplets into its matrix, the coating prevents light from scattering. It works well even after a year of storage in the dark, Rubner reported.

Glaring Improvement

Such coatings hold promise beyond preventing fog, according to Paula T. Hammond, an MIT materials scientist who was not involved in the research.

A water-absorbent coating could be used as a primer on usually impermeable surfaces, allowing them to absorb such substances as ink, for example.

Hammond added that "it might make it easier to apply things like flexible electronics on plastic surfaces."

Rubner already has multiple uses in mind for his glass-treatment technique. In addition to its extreme absorbency, the coating reflects less light than the surface of untreated glass, thereby reducing glare and letting more light through.

That suggests it could enhance the light-capturing capabilities of camera lenses and solar-powered voltaic cells, Rubner said. When part of a sheet of glass is surfaced with the new coating, it becomes remarkably transparent, he noted. "The half that's not coated actually looks dirty."

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