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Clean as a whistle. A plastic embedded with nanoparticles repels sludgy shampoo, so that every last drop slides easily out of the bottle. The nanoparticles are made out of cheap silica – a component of sand – so the new material could be mass produced.

Losing a bit of hair product might seem like a petty annoyance, but it’s actually a serious environmental problem, says at the Ohio State University in Columbus. “You throw the bottle away and you still have these harsh chemicals in the bottle.”

It’s relatively easy to repel water-based liquids like juice or ketchup from plastic. Such liquids have high surface tension, so their molecules stick to each other instead of the bottle surface. By contrast, liquids like shampoos, soaps and detergents have low surface tension and so tend to stick to the side or cap of the bottle.

To create a slippery surface, Bhushan and his colleagues put silica nanoparticles into a liquid called xylene and spun and heated it up in a chamber with a piece of plastic, to simulate a real bottle.

The nanoparticles crash into the hot plastic and embed themselves in it, forming hooked structures that rise above the plastic surface. As the plastic cools, it reforms around the silica bits, holding them tight.

Finally, the team treated the surface with UV light and coated it with a chemical called fluorosilane, which is a neutral molecule that doesn’t grab onto liquids.

The silica and fluorosilane hooks keep liquids away from the plastic surface. Silica doesn’t attract liquids, so the shampoo molecules don’t get stuck and can slide easily across the bumpy surface of the bottle.

Decreasing the amount of shampoo wasted would save a lot of resources, says at the University of Illinois in Chicago. A percent or two of product is lost in each bottle. “If you think about just a single bottle, it would seem not a big deal,” he says. “But if you think about billions of bottles, then it all adds up and it can make a huge difference.”

The material’s developers did a good job at turning a clever idea into a usable technology, says at the University of Wisconsin in Milwaukee. “The principle is known and was suggested some 10 years ago, but it is not easy to produce,” he says. “It looks like a nice advancement.”

The technology has uses outside the shower, Bhushan says. Liquid-repellant surfaces could help make sterile surfaces for medical supplies and food packaging, since bacteria won’t be able to cling to the plastic. “There could be many applications,” he says.

Journal reference: Philosophical Transactions of the Royal Society A, DOI: 10.1098/rsta.2016.0135

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