Floating weed inspires high-tech waterproof coating

A plastic material inspired by the leaves of the aquatic weed Salvinia molesta may lead to a coating that makes ships more buoyant and hydrodynamic (Photo: Eric Guinther)

It may be an invasive weed that's fouling waterways in the U.S., Australia and other countries, but it turns out that Salvinia molesta has at least one good point - it's inspired a man-made coating that could help ships stay afloat. The upper surface of the floating plant's leaves are coated with tiny water-repellent hairs, each of which is topped with a bizarre eggbeater-like structure. These hairs trap a layer of air against the leaf, reducing friction and providing buoyancy, while the eggbeaters grab slightly at the surrounding water, providing stability. Scientists at Ohio State University have successfully replicated these hairs in plastic, creating a buoyant coating that is described as being like "a microscopic shag carpet."

In laboratory tests, the man-made coating performed just like the Salvinia hairs. In both cases, water droplets couldn't penetrate between the hairs, but did cling to the uniquely-shaped tips - they even hung on when the surface was tilted by 90 degrees. The adhesive force of the coating was measured at 201 nanoNewtons (billionths of a Newton), while the natural hairs managed an almost identical 207 nanoNewtons. While these numbers are far below those attained by substances such as adhesive tape, they are similar to those of gecko feet - and geckos seem to have no problem climbing walls.
"I've studied the gecko feet, which are sticky, and the lotus leaf, which is slippery," said lead researcher Bharat Bhushan. "Salvinia combines aspects of both."

If commercialized, the Ohio State-developed material could conceivably be applied to the hulls of ships or submarines. It is believed that it could provide the vessels with more flotation, while helping them sit in the water with more stability and move through it more easily.
A paper on the research was recently published in the Journal of Colloid and Interface Science.