Thursday, February 23, 2006

Super-Repellent Plastic

With GE's new plastic, self-washing buildings, cheap diagnostic chips, and free-flowing honey jars are possible.

By David Talbot

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If you've ever despaired over getting the last drop of ketchup or detergent out of a plastic bottle -- or happen to be a microfluidics researcher wondering how you'll ever mass-produce a cheap diagnostics chip -- scientists at GE may have a plastic for you.

Company researchers have come up with a way to process a common polymer so that it repels fluid, even drops of honey roll right off. The resulting property is called "superhydrophobicity" -- or extreme repelling of water-based fluids -- beyond even that of a freshly waxed car.

[Click here to view images.]

While several existing engineered materials behave this way, the GE accomplishment is noteworthy because it was done with an inexpensive plastic, GE's Lexan, that's normally "hydrophilic," meaning water spreads out on contact, not something that's "hydrophobic" to start with, such as Teflon or silicone-based materials. These latter materials are far more expensive compared with Lexan, a ubiquitous thermoplastic used in products ranging from CDs and DVDs to automotive headlamps, food storage containers, and common household appliances.

While GE is not predicting specific applications yet, a few are theoretically possible. A cheap superhydrophobic plastic could be used in food containers from which every last bit of ketchup or syrup would flow right out. It could also allow for a building panel that repels water so efficiently that rain would wash away dirt -- making it essentially self-cleaning.

Such a material could be a bonanza for medicine, too. In the field of microfluidics, superhydrophobic materials are needed so that tiny volumes of blood or other body fluids can flow more easily through micrometer-scale channels. Although some superhydrophobic materials are currently available, they're expensive enough to preclude visions of diagnostic gadgets that you could buy in a drugstore. A cheap plastic, though, could make such a disposable diagnostic chip feasible. "It is a big deal and it is important for the microfluidics applications," says Neelesh Patankar, a mechanical engineer and microfluidics at Northwestern University.

Super-Repellent Plastic

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