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Topping Teflon

Making flexible coatings with increased water-resistance and durability is a snap--literally, according to a report published today in the journal Science. Chemically attaching coating molecules to a polymer material that has been stretched, and then letting that material snap back into shape creates a nearly impenetrable layer that could eventually be used to coat everything from frying pans to airplanes.

Jan Genzer and Kirill Efimenko of North Carolina State University embedded fluorinated molecules, which are commonly found in the polymer surfaces of non-stick pans and water-repellant fabrics, into a silicone rubber-like polymer known as polydimethyl siloxane. The result was a so-called mechanically assembled monolayer (MAM). In subsequent tests of the material's impermeability and durability, the researchers submerged strips of MAM and strips of traditional coatings in water and then stored them under normal lab conditions. "To our surprise, the surfaces of MAMs stayed virtually unchanged, even after six months in a dusty, humid atmosphere. The MAMs' chemical properties, such as orientation and molecular density, remained the same, and there was very little physical deterioration," Genzer notes. The standard coating, on the other hand, began to deteriorate after sitting in the water for a relatively short period of time. "Their molecules become disorganized. In some cases, we have observed that surface properties are degraded after barely more than a day," he added.

The team plans to follow up on these promising initial results by experimenting with hydrocarbons as the embedded molecules, and exploring the MAM coating's performance in acid and other extreme environments. "By manipulating materials at the nanoscale, we can vastly improve on what Mother Nature offers, Genzer remarks, "for the benefit of both manufacturers and consumers."

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