New materials repel oil under water and under duress
UW-Madison researchers have announced a significant step forward in the development of materials that can ward off oil.
While Vilas Distinguished Achievement Professor of Chemical and Biological Engineering David Lynn and assistant scientist Uttam Manna didn’t initially set out to develop highly oleophobic (oil-repelling) materials, they identified a unique opportunity stemming from their group’s combination of chemistry expertise and experience in fine-tuning the nano- and micro-scale structures of materials. In a new paper in the journal Advanced Functional Materials, Manna and Lynn describe new coatings that are extremely oil-repellant (or “superoleophobic”) in underwater environments and retain that property even when subjected to physical abrasion. Potential applications of this discovery range from protective anti-fouling coatings for objects in aqueous or marine environments to new approaches to cleaning up oil spills and separating fine chemicals.
Manna says a unique, layer-by-layer approach to fabricating thin, multi-layer polymer films allowed the researchers to manipulate both the chemistry and the topography of the material, yielding three-dimensional structures that are porous at the micrometer and nanometer scale.
And in a significant advance with respect to practical utility, these porous materials remain superoleophobic even when damaged. In one test, the researchers coated a glass slide with their superoleophobic film and abraded a section of the coating with sandpaper. The damaged areas continued to repel droplets of oil, which remained suspended above the surface in an ellipsoid shape, just as effectively as the untouched areas. The researchers also placed the film in boiling water, scratched it, froze it, and stuck tape to it and ripped it off. Even when they succeeded in damaging the material, the researchers found they didn’t break down the porous structure that makes it oleophobic.
“If you remove the top surface, the under-surface still satisfies the physical and chemical criteria,” Manna says. This property is unique, and marks an advance toward the development of oil-repellant coatings that can withstand the rigors of use in applied settings.
The coatings also held up in simulated seawater, lake water, and the presence of proteins and other surface-active contaminants. “This feature addresses some of the problems with other types of ‘super-phobic’ surfaces,” says Lynn. “Once you put them out in the real world, they stop working.”
And in the real world, these materials could provide solutions to tricky problems. “One of the major motivations for me to work on this particular problem is its ability to work in a marine environment,” Manna says, citing the 2010 oil spill in the Gulf of Mexico.
In fact, the researchers found that the material can be used to easily separate oil and water. In one test, they coated wire mesh with the material, then poured a mixture of water and motor oil through it. The water passed through, and nearly all of the oil accumulated on top of the mesh, allowing it to be easily collected and recovered. The effectiveness of this simple process, and the ability to tune the properties of these materials, points to potential applications in all manner of situations where one chemical needs to be separated from another.
“We’re not just talking about the potential to develop new tools to help clean up oil spills,” Lynn says. “It could also be fragrances and pharmaceuticals, fine chemicals, or other organic liquids.”
The researchers say the next challenge is to translate the lessons learned from these new materials into a viable process for creating new oil-repellant coatings on larger scales.
“We’ll find, over time, that there are better ways of making materials that have these same physical and chemical properties,” Lynn says. “With the principles that we’ve uncovered, we can now to go back and try to do on purpose what we discovered by accident. And find a way to make it scalable."
The research was funded by the Office of Naval Research and the UW-Madison Materials Research Science and Engineering Center (MRSEC).