COLUMBUS, Ohio β A floating weed that clogs waterways around the world has at least one redeeming feature: Itβs inspired a high-tech waterproof coating intended for boats and submarines.
The Brazilian fern Salvinia molesta has proliferated 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 November 1 issue of 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 fibers. The plastic coating they created in the laboratory is soft and plush, like a microscopic shag carpet.
In nature, air pockets trapped at the base of Salviniaβs hairs reduce friction in the water and help the plant float, while a sticky region at the tips of the eggbeaters clings lightly to the water, providing stability.
Itβs the combination of slippery and sticky surfaces that makes the texture so special, said Bharat Bhushan, Ohio Eminent Scholar and the Howard D. Winbigler Professor of mechanical engineering at Ohio State.
βThe Salvinia leaf is an amazing hybrid structure. The sides of the hairs are hydrophobic β in nature, theyβre covered with wax β which prevents water from touching the leaves and traps air beneath the eggbeater shape at the top. The trapped air gives the plant buoyancy,β he said.
Thatβs a very tiny force compared to familiar adhesives such as transparent tape or even masking tape. But the adhesion is similar to that of another natural surface studied by Bhushan and other researchers: gecko feet.
βIβve studied the gecko feet, which are sticky, and the lotus leaf, which is slippery,β Bhushan said. βSalvinia combines aspects of both.β
Bhushan develops biomimetic structures β artificial structures created in the lab to mimic structures found in nature. The gecko feet inspired him to investigate a repositionable, βsmartβ adhesive, and the lotus leaf inspired the notion of glass that repels water and dirt.
He came to study Salvinia through a colleague in the universityβs Biological Sciences Greenhouse, who provided samples of the plant for the study.
Salvinia molesta, also known as giant salvinia, is native to Brazil, and is a popular plant for home aquariums and decorative ponds around the world. It needs no dirt, but lives solely in the water β even moving water such as rivers and lakes.
At some point, the hearty plant escaped from peopleβs homes into the wild. Now it has proliferated into commercial waterways in North America, South America, and Australia, where it has become an invasive species.
While the plant is a nuisance to ships today, it could ultimately provide a benefit if a commercial coating based on its texture became available. Bhushan has no plans to commercialize it himself, though.
βWith this study, weβve gotten deep insight into a very simple concept [how the Salvinia leaf works]. Thatβs where the fun is,β he said. βBesides, Iβve already moved on to studying shark skin.β
Contact: Bharat Bhushan, (614) 292-0651; [email protected] Written by Pam Frost Gorder, (614) 292-9475; [email protected]
Contact: Bharat Bhushan [email protected] 614-292-0651 Ohio State University
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