Engineered surfaces are ‘most water-resistant ever’

The team from MIT began by analysing the wings of the Morpho butterfly and the veins of nasturtium leaves. They found that drops of water bounced off both the leaves and the butterfly wings faster than they bounced off lotus leaves, which are often considered the 'gold standard' of ultra dry, water-resistant surfaces. The reason? Tiny ridges on their surfaces that can make bouncing droplets form non-uniform shapes, which causes them to spend less time in contact with a surface. In tests, the team applied the same ridges to aluminium and copper oxides, and found that they repelled water 40% faster than the lotus leaf. At super-cooled temperatures, water even bounced off the metals before it had time to freeze. By applying the same patterns to other metals, fabrics and ceramics, the researchers hope to inspire a new generation of water, and potentially ice-resistant wind turbines and aircraft engines. "We've demonstrated that we can use surface texture to re-shape a drop as it recoils, in such a way that the overall contact time is significantly reduced," said James Bird, an assistant professor of mechanical engineering at Boston University, who worked on the project. "The upshot of this," he continued, "is that the surface stays drier longer if this contact time is reduced, which has the potential to be useful for a variety of applications." Speaking to BBC News, lead researcher Kripa Varanasi, an associate professor of mechanical engineering at MIT, said the plan now is to take the concept and optimise it to produce even more water-resistant structures. "I hope we can manage to get a 70 to 80% reduction [in contact time]," he said. "There's a lot of room left."