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Super water-repellent film
Dennis Normile, Roy OConnor, Bruce Wiebushc, Norman Bartlett -- Design News, July 16, 2001
Researchers at Osaka Prefecture University in Japan have developed a new low-temperature process that allows even heat-sensitive materials to be coated with a transparent super water-repellent film. The Osaka Prefecture University group, led by Materials Scientist Tsutomu Minami, had previously developed a method of forming a transparent highly water-repellent film. That process deposits a thin film of alumina, mixed with an organic resin, on a substrate and then bakes the object at 400C. The heat burns off the organic molecules, producing a regular surface roughness with features on the scale of tens of nanometers—enough to get the desired shape effect yet with sufficient consistency to minimize loss of transparency due to light dispersion. The alumina is then coated with a film of hydrolyzed fluoroalkyltrimethoxysilane (FAS), a water-repellent. Unfortunately, the high temperatures required make this method only suitable for such temperature-resistant materials as glass and ceramics. The new method relies on a chemical reaction rather than high temperature. The object is first coated with an alumina gel film chemically modified with acetoacetic acid. When immersed in a water bath at 60C, the chemicals react, forming tiny crystals which are washed off to create the minutely rough surface. The surface is then coated with FAS as in the heat-treatment process. Since it is a low-temperature process, the researchers believe it could be used for ski goggles and motorcycle helmet visors, where highly water-repellent yet transparent coatings are needed for plastic substrates. For additional details, contact Tsutomu Minami, Dept. of Applied Materials Science, Graduate School of Engineering, Osaka Prefecture University, Japan. Tel: +81 722 54 9329; Fax: +81 722 54 9913; or e-mail minami@ams.osakafu-u.ac.jp.
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