Clogging weed inspires waterproof coating for boats

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A floating weed that clogs waterways around the world has led to the development of a high-tech waterproof coating intended for boats and submarines.

The Brazilian fern Salvinia molesta has flourished around the Americas and Australia in part because its surface is dotted with oddly shaped hairs that trap air, reduce friction and help the plant stay afloat.

In the Journal of Colloid and Interface Science, Ohio State University engineers describe how they recreated the texture, which resembles a carpet of tiny eggbeater-shaped fibres.

In nature, air pockets trapped at the base of Salvinia’s hairs reduce friction in the water and help the plant float, while a sticky region at the tips of the eggbeaters provides stability by clinging to the water.

It’s the combination of slippery and sticky surfaces that makes the texture so special, said Bharat Bhushan, professor of mechanical engineering at Ohio State University.       

’The Salvinia leaf is an amazing hybrid structure. The sides of the hairs are hydrophobic — in nature, they’re covered with wax — which prevents water from touching the leaves and traps air beneath the eggbeater shape at the top. The trapped air gives the plant buoyancy,’ he said.

’But the tops of the hairs are hydrophilic. They stick to the water just a tiny bit, which keeps the plant stable on the water surface.’

Bhushan and masters student Jams Hunt compared the stickiness of their plastic coating with the stickiness of the natural Salvinia leaf using an atomic-force microscope. The two surfaces performed nearly identically, with the plastic coating generating an adhesive force of 201 nanonewtons and the leaf generating 207 nanonewtons.

That’s a very small force compared with familiar adhesives such as transparent tape or even masking tape.

With commercial development, the coating could reduce drag and boost buoyancy and stability on boats and submarines, Bhushan said.