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New Nanocoating Foils Fog
29 August 2005 (All day)
WASHINGTON, D.C.--Blasting your car's defroster on a cold morning may soon go the way of the horse and buggy. A team of researchers has come up with a way to create a permanent antifogging coating on a wide variety of surfaces. Because the new coating is both cheap and durable, it could find its way onto car windshields, glasses, and other surfaces within the next 2 to 5 years.
Antifog coatings are nothing new, but current varieties have their drawbacks. Commercial sprays, for example, wear off and must be reapplied. Researchers have also recently developed glass containing titanium dioxide particles that reduce fogging, but these only work in daylight.
In hopes of finding a more broadly applicable solution, Massachusetts Institute of Technology materials scientist Michael Rubner and colleagues turned to multilayered films of polymers and glass nanoparticles. They create their films by alternately dipping a glass slide in a solution containing soluble negatively charged glass nanoparticles and a positively charged polymer they've dubbed "poly" (it's actually allylamine hydrochloride). The process creates a porous network of glass nanoparticles glued together by the polymers. The researchers then heat the slide to 500 degrees Celsius, burning off the polymer and fusing the glass particles together in an extended porous network.
The nanoparticles in the new coating foil fog by preventing the formation of tiny water droplets on the surface of glass that scatter light in random directions. When water begins to condense on the coating, it is strongly attracted to hydroxyl groups on the glass particles. The water is then wicked into the porous layer, causing it to form a uniform, transparent sheet.
The coating may have another use, too. Rubner, who described the findings here today at a meeting of the American Chemical Society, showed that by patterning the water hugging material, his team could steer water to flow in specified directions across a surface. That could enable researchers to create tiny chip-scale "microfluidic" instruments to move liquids across surfaces without actually having to carve tiny channels.
Pierre Schaff, a polymer multiplayer expert at the University of Strasbourg in France, calls the new work very exciting because it offers the first potentially permanent antifogging coating. "It's very easy to create these films, and they are potentially very durable," Schaff says. Rubner says representatives from three car companies have already expressed interest in using the technique to create nonfogging windshields.
Rubner's home page