Somebody once said that necessity is the mother of invention, This old proverbial saying that is often ascribed to Plato though uncertainty still clouds its origin, has a lot to do with the developments we see everyday. Whenever there is an oil spill like the one that happened in the Gulf of Mexico from the Deepwater Horizon sometime back, the oil has to be spread to a larger area if it cannot be collected back and purified. This is to ebb the extent of the damage to sea life that it causes around that area as it is believed that if spread, the resultant effect would be minimized. Normally, the process of dispersing uses chemicals called surfactants that end up harming the sea life again- looks like a double tragedy, right?
Relief now comes whereby a method of filtering has been developed that can pull oil out of the water without any use of chemicals. The filter has a shape-shifting surface with a coating that simultaneously attracts water while at the same time repelling the oil. This is the opposite of the character that has been found in many materials that have been soaking up the oil and repelling water-attributed to the high surface tension of water compared to that of oil hence it tends to bead up before oil. Obviously, any material that ends up repelling oil is most likely to paint water with the same brush i.e. repel it too.
This wonderful material that contravenes heresy is the product of the work of material scientists Anish Tuteja(Assistant Professor of materials science and engineering) and Arun Kota from the University of Michigan and was the upshot of blending together an ordinary polymer and a new type of nanoparticles called fluoroPOSS. According to Tuteja, fluoroPOSS is a cage of silicon and oxygen surrounded by molecules similar to Teflon. It is hydrophilic, so it loves water but is also oleo phobic (hates oil). The researchers coated the filter with a rubbery commercially available polymer and nanoparticles then put it in water mixed with oil. The nanoparticles, due to their low surface energy, cause oil particles to attract each other more and more hence they bead up. The water is strongly attracted to the polymer and forms hydrogen bonds with it hence gets wicked away just like a paper towel soaking up water. The technique heavily capitalizes on the fact that the capillarity action of water is different from that of oil such that the oil will lag behind but the simplicity of the process-just based on gravity actually marveled me. As Tuteja puts it, “These results were at first surprising, and they're possible because of a particularly nifty property of the new coating. When it is exposed to water, the polymer and the nanoparticle components scamper into a different configuration---one that encourages the water molecules to bond with the polymer”.
Arun Kota, a postdoctoral researcher in materials science and engineering and the first author of the paper titled "Hygro-responsive membranes for effective oil-water separation." Said that,"The polymer, in essence, reaches up during surface reconfiguration through the filter and wicks more water across, while the oil remains above the filter”.
Tests were carried using a variety of oil mixes and it proved a 99.9% efficiency in the separation of oil from water. Another advantage of the process was the period that the coated filters worked before they got clogged-100hrs. This means it is easy to maintain as it did not require too much attention. Moreover, even if chemicals are added to the oil as it was done in the Gulf of Mexico, the oil can still be separated from the water. This group’s reseach was supported by the Scientific Research office of the Air Force and the results, authoured by Anish Tuteja published in the August 28th issue of Nature communications. You can look at the process at the University of Michigan. It is also interesting to watch the video here.
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