Dispersing oil that spills into the ocean, for instance the oil that exploded in the Gulf of Mexico from Deepwater Horizon, involves chemicals called surfactants, which can harm local sea life. Now, a filter has been developed that can pull oil out of water, no chemicals required.
The filter has a coating that repels oil, but attracts water. Most materials do the reverse -- soak up oil and repel water. That's because the surface tension of water is higher than oil's. Water tends to bead up before oil. And typically any material that repels oil is likely to repel water as well.
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But Anish Tujeta, and Arun Kota, materials scientists at the University of Michigan, made a material that works in a counterintuitive way. They blended together an ordinary polymer and a new kind of nanoparticle called fluoroPOSS.
"On a molecular level, the nanoparticle is essentially a cage of silicon and oxygen surrounded by molecules similar to Teflon," Tujeta told Discovery News.
The scientists coated a filter with the polymer and nanoparticles and then dipped it into water mixed with oil. The nanoparticles have a low surface energy that causes oil droplets to become strongly attracted to each other. The attraction causes the oil to bead up. But the water is strongly attracted to the polymer and gets wicked away like a paper towel soaking up water. Oil and water's capillary action is quite different, which is why the oil gets left behind. The entire process happens using just gravity – there's no need to force water across the filter surface.
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The group tested a variety of oil and water mixes, and even mayonnaise. They were able to separate water from oil with 99.9 percent efficiency, and the coated filters worked for up to 100 hours before they got clogged.
The research was supported by the Air Force Office of Scientific Research, and the results were published in the Aug. 28 issue of Nature Communications.