Nanocoating Could Eliminate Foggy Windows And Lenses

Thetransparent coating can be applied to eyeglasses, camera lenses, skigoggles … even bathroom mirrors, they say. The new coating wasdescribed today at the 230th national meeting of the American ChemicalSociety, the world’s largest scientific society.

Researchers havebeen developing anti-fog technology for years, but each approach hasits drawbacks. Some stores carry special anti-fog sprays that helpreduce fogging on the inside of car windows, but the sprays must beconstantly reapplied to remain effective. Glass containing titaniumdioxide also shows promise for reduced fogging, but the method onlyworks in the presence of ultraviolet (UV) light, researchers say.

"Ourcoatings have the potential to provide the first permanent solution tothe fogging problem," says study leader Michael Rubner, Ph.D., amaterials science researcher at MIT in Cambridge, Mass. "They remainstable over long periods, don’t require light to be activated and canbe applied to virtually any surface." Coated glass appears clearer andallows more light to pass through than untreated glass whilemaintaining the same smooth texture, he says.

The coatingsconsist of alternating layers of silica nanoparticles, which arebasically tiny particles of glass, and a polymer called polyallylaminehydrochloride, both of which are relatively cheap to manufacture,Rubner says. He has applied for a patent on the manufacturing processand says that the coating could be available in consumer products intwo to five years. The military and at least two major carmanufacturers have already expressed interest in using the technology,he says.

When fogging occurs, thousands of tiny water dropletscondense on glass and other surfaces. The droplets scatter light inrandom patterns, causing the surfaces to become translucent or foggy.This often occurs when a cold surface suddenly comes into contact withwarm, moist air.

The new coating prevents this process fromoccurring, primarily through its super-hydrophilic, or water-loving,nature, Rubner says. The nanoparticles in the coating strongly attractthe water droplets and force them to form much smaller contact angleswith the surface. As a result, the droplets flatten and merge into auniform, transparent sheet rather than forming countless individuallight-scattering spheres. "The coating

basically causes water that hits the surfaces to develop a sustained sheeting effect, and that prevents fogging," Rubner says.

Thesame coatings also can be engineered to have superior anti-reflectiveproperties that reduce glare and maximize the amount of light passingthrough, an effect that shows promise for improving materials used ingreenhouses and solar cell panels, the researcher says. So far, thecoating is more durable on glass than plastic surfaces, but Rubner andhis associates are currently working on processes to optimize theeffectiveness of the coating for all surfaces. More testing is needed,they say.

Funding for this study was provided by the DefenseAdvanced Research Projects Agency (DARPA) and the National ScienceFoundation (via the Materials Research Science and Engineering Centers,or MSREC).

The American Chemical Society is a nonprofitorganization, chartered by the U.S. Congress, with a multidisciplinarymembership of more than 158,000 chemists and chemical engineers. Itpublishes numerous scientific journals and databases, convenes majorresearch conferences and provides educational, science policy andcareer programs in chemistry. Its main offices are in Washington, D.C.,and Columbus, Ohio.