Nanotechnology

On a Wet Day You Can See Forever

A foggy windshield can drive a motorist nuts. The thousands of tiny water droplets that form on the glass scatter light, making oncoming traffic hard to see. Most solutions don't work: Antifogging sprays are short lived, and windshields coated with titanium dioxide require exposure at least every few hours to either ultraviolet or visible light

Courtesy Michael Rubner/MIT
Antifogging glass covers the
lower left area of this photo. The
right and top have normal glass.

To address the fog problem anew, materials scientist Michael Rubner and his colleagues at MIT turned to nanotechnology and recently announced the development of a permanent glass coating that keeps fog from forming on windshields. Rubner used nanoparticles made of silica, the same material glass is made of, to create a coating with a rough surface. Although the coating looks smooth to the naked eye, it actually contains 10 to 20 layers of particles, each only seven nanometers in diameter, with air pockets between the particles. Because the silica particles attract water, "when you put a droplet on that surface, the water is drawn into these pores instantaneously and wicked away into a uniform sheet," Rubner says.



An Australian company called XeroCoat is already a lap ahead with a similar product. The company's founders, Paul Meredith and Michael Harvey, used porous silica to make permanent antifogging coatings that work on various plastic products as well as on glass. Rubner's coating requires curing at 932 degrees Fahrenheit, too hot for most plastics.


The coatings made by both groups are antireflective as well as antifogging: They reduce glare and allow more than 99 percent of light to pass through the glass. (Normal glass scatters about 8 percent of light.) The basic materials for both products are dirt cheap, Rubner says, and the manufacturing process is simple. Before long, we may all be driving a little more safely, and sanely.