Skip to comments.ScienceShot: Water Floats on Oil
Posted on 04/07/2012 10:37:07 PM PDT by neverdem
Two years ago, the explosion of the Deepwater Horizon oil rig covered hundreds of square miles of the Gulf of Mexico with oil (main image). The oil floated because it is less dense, and therefore lighter, than water. But now scientists say that water can sometimes float on oil—and their findings, which were published last month in Langmuir, could help to mop up oil slicks like the one created by the 2010 disaster. Using a theoretical model, the scientists calculated the forces acting on water when it is dripped onto an oil surface. Taking into account surface tension, the property that allows some insects to walk on water, they showed that a water droplet can "hang" from the oil's surface. The oil surface droops like a rubber membrane, allowing the above air—which is much lighter than oil and water—to extend beneath the surface's average level. With help from the surface tension, this air pocket balances the weight of the water droplet, preventing it from sinking. The scientists confirmed the model's predictions in tests and found that water droplets up to 170 microliters in volume could float on oil (inset image and video). Such water droplets would be large enough to harbor natural microbes that consume oil. If they were sprayed over an oil slick, the scientists say, the cleanup process could be much faster.
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170 microliters is quite a bit larger than most drops of water. This is the size achieved under controlled laboratory conditions; I wonder what size would be attainable in real world conditions? Also, they mentioned that they foresee mixing hydrocarbon consuming bacteria in with the water and then spraying it over an oil slick. I wonder what bacteria would do to the surface tension? Could they act like a surfactant, in which case making drops like the one shown would be much more difficult? So many questions...
There are many oils heavier than water. In a salt water environment, where water is 7 API, it would remain above most common residual oils (Number 6 or Number 5 oil in common parlance.) There are heavy refinery cuts reaching down to negative 4 API.
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