New durable, hydrophobic coating makes steel stronger
Harvard-developed tungsten oxide coating could have applications ranging from medical instruments to ship hulls.
“Our slippery steel is orders of magnitude more durable than any anti-fouling material that has been developed before,” said Joanna Aizenberg, the Amy Smith Berylson Professor of Materials Science and core faculty member of the Wyss Institute for Biologically Inspired Engineering at Harvard University.
“So far, these two concepts – mechanical durability and anti-fouling – were at odds with each other. We need surfaces to be textured and porous to impart fouling resistance but rough nanostructured coatings are intrinsically weaker than their bulk analogs. This research shows that careful surface engineering allows the design of a material capable of performing multiple, even conflicting, functions, without performance degradation.”
Made from rough nanoporous tungsten oxide, the coating (Slippery Liquid-Infused Porous Surfaces or SLIPS for short) derives its resiliency from the process by which the steel is coated. Using an industry standard electrochemical technique, an ultrathin film, made up of hundreds of thousands of small and rough tungsten-oxide islands, is grown directly onto a steel surface.
“If one part of an island is destroyed, the damage doesn’t propagate to other parts of the surface because of the lack of interconnectivity between neighboring islands,” said Alexander B. Tesler, former postdoctoral fellow at SEAS, current research fellow at Weizmann Institute of Science in Israel and the paper’s first author. “This island-like morphology combined with the inherent durability and roughness of the tungsten oxide allows the surface to keep its repellent properties in highly abrasive applications, which was impossible until now.”
Although discovered in 2011, the Harvard team has spent the last five years testing the coating’s potential commercial applications. On the smaller scale, for example, the team tested a tungsten oxide coated scalpel that repels blood but the material could just as easily be applied to any instrument or implant capable of transmitting pathogens. By scaling the process up, the researchers say the coating could also save militaries million by repelling barnacles and other organisms from the hulls of ships.