How Hendrik Hoelscher and Matthias Worgull want to clean up the oceans.
Today, 25 years after the oil tanker accident of Alaska, the name Exxon Valdez still stands for one of the biggest environmental disasters in maritime history. After the ship struck a reef, 37,000 tons of crude oil spilled into the open sea, contaminating more than 2,000 kilometers of coastline. Oil spills on the open sea are not an isolated incident: large quantities of crude oil or mineral oil repeatedly spill into the sea from damaged tankers, pipelines or oil platforms.
In elaborate large-scale technical operations, attempts are made to remove oil spills and contain consequential damage – however, these measures often involve the risk of additional environmental pollution and have not been very effective so far. Scientists from KIT have found a way to quickly and cleanly remove oil from the oceans. To do so, they have copied a trick from nature.
Salvinia, an inconspicuous tropical floating fern, has an amazing property: The plant can remain completely dry under water. This is possible because of microhairs that form a thin film of air around the entire leaf. This Salvinia®-effect was discovered by the well-known bionics expert Prof. Wilhelm Barthlott and further detected together with Prof. Thomas Schimmel from Karlsruhe.
Hendrik Hoelscher and Matthias Worgull, both researchers at KIT, were inspired by the Salvinia®-effect and started experimenting to reproduce the plant's tiny hairs using microstructure technology in 2012. A coincidence in the lab led to a slightly different arrangement of hairs and craters – which, unlike the Salvinia plant, not only keeps water out, but additionally absorbs oil particularly well. "Films with such a surface structure are what we call nano-fur. Immersed in an oil-water mixture, it removes the oil components quickly and without environmental pollution," explains physicist Hoelscher.
"Innovations sometimes occur in a roundabout way. We discovered the benefit of our nanostructure when we were actually researching something else."
Different methods are currently used to remove an oil spill: Burning the oil and accelerating natural decomposition by adding dispersants entail a questionable environmental impact and health risks. Therefore, the oil slick is skimmed off whenever possible. Natural materials are used to separate the oil-water emulsion, for example sawdust. However, these absorb more water than oil and are thus not effective enough. Alternative commercially available materials, such as foams or polypropylene mats, absorb oil to a high degree, but are either highly flammable, unstable, or do not retain the oil long enough.
The nano-fur does not have any of these disadvantages and is relatively easy to produce for this purpose, according to Hoelscher: "In order to emboss a plastic film accordingly, a mold insert, a stamp so to speak, is produced. To do this, a steel plate is sandblasted to create tiny craters on a nanometer scale. A polymer film is inserted into the mold insert, and the steel mold is heated. If this is removed while still heated, the warm plastic pulls threads, similar to cheese on a pizza. This is how the required irregular hair structure is created."
The prototype of the nano-fur is still too small for use on the high seas, but Hoelscher and Worgull are working on a large-scale production: "According to our test results, an investment in the nano-fur would be worthwhile for both, companies and the environment."