Plant with 'eggbeater' testure inspires waterproof coating

Nov 10, 2011
A drop of water sits atop eggbeater-shaped hairs on a Salvinia molesta leaf. Credit: Image courtesy of Ohio State University.

A floating weed that clogs waterways around the world has at least one redeeming feature: It's 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 and Interface Science, Ohio State University engineers describe how they recreated the texture, which resembles a carpet of tiny eggbeater-shaped . 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 Salvinia's hairs reduce 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.

It's 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 at Ohio State.

"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."

This is an optical micrograph of eggbeater-shaped hairs on the leaf surface of the aquatic plant Salvinia molesta. The hairs reduce friction and help the plant stay afloat. Ohio State University engineers have replicated the surface in a plastic coating that could reduce drag and boost buoyancy on boats and submarines. Credit: Image courtesy of Ohio State University.

In tests, the coating performed just as the Salvinia hairs do in nature. The bases of the hairs were slippery, while the tips of the hairs were sticky. Water droplets did not penetrate between the hairs, but instead clung to the tops of the eggbeater structures – even when the coating sample was turned on its side to a 90-degree vertical.

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

Bhushan and master's student Jams Hunt compared the stickiness of their plastic coating to 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 (billionths of a Newton) and the leaf generating 207 nanoNewtons.

That's 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.

"I've studied the gecko feet, which are sticky, and the lotus leaf, which is slippery," Bhushan said. "Salvinia combines aspects of both."

Bhushan develops biomimetic structures – artificial structures created in the lab to mimic structures found in nature. The gecko feet inspired him to investigate a repositionable, "smart" 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 university's 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 – even moving such as rivers and lakes.

At some point, the hearty plant escaped from people's homes into the wild. Now it has proliferated into commercial 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 based on its texture became available. Bhushan has no plans to commercialize it himself, though.

"With this study, we've gotten deep insight into a very simple concept [how the Salvinia leaf works]. That's where the fun is," he said. "Besides, I've already moved on to studying shark skin."

Explore further: Making graphene in your kitchen

Related Stories

Bionic coating could help ships to economize on fuel

May 04, 2010

The hairs on the surface of water ferns could allow ships to have a 10 per cent decrease in fuel consumption. The plant has the rare ability to put on a gauzy skirt of air under water. Researchers at the University of Bonn, ...

Nature helps to solve a sticky problem

Apr 05, 2011

The arrays of fine adhesive hairs or 'setae' on the foot pads of many insects, lizards and spiders give them the ability to climb almost any natural surface. Research by James Bullock and Walter Federle from the University ...

Recommended for you

Making graphene in your kitchen

48 minutes ago

Graphene has been touted as a wonder material—the world's thinnest substance, but super-strong. Now scientists say it is so easy to make you could produce some in your kitchen.

Thinnest feasible nano-membrane produced

Apr 17, 2014

A new nano-membrane made out of the 'super material' graphene is extremely light and breathable. Not only can this open the door to a new generation of functional waterproof clothing, but also to ultra-rapid filtration. The ...

Wiring up carbon-based electronics

Apr 17, 2014

Carbon-based nanostructures such as nanotubes, graphene sheets, and nanoribbons are unique building blocks showing versatile nanomechanical and nanoelectronic properties. These materials which are ordered ...

Making 'bucky-balls' in spin-out's sights

Apr 16, 2014

(Phys.org) —A new Oxford spin-out firm is targeting the difficult challenge of manufacturing fullerenes, known as 'bucky-balls' because of their spherical shape, a type of carbon nanomaterial which, like ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

El_Nose
5 / 5 (2) Nov 11, 2011
basically all they did was radically increase the surface area of an object and they are surprised at it's buoyancy??

More news stories

Making graphene in your kitchen

Graphene has been touted as a wonder material—the world's thinnest substance, but super-strong. Now scientists say it is so easy to make you could produce some in your kitchen.

Low tolerance for pain? The reason may be in your genes

Researchers may have identified key genes linked to why some people have a higher tolerance for pain than others, according to a study released today that will be presented at the American Academy of Neurology's 66th Annual ...

How to keep your fitness goals on track

(HealthDay)—The New Year's resolutions many made to get fit have stalled by now. And one expert thinks that's because many people set their goals too high.