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Scientists (finally) get all of that shampoo out of the bottle

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A newly developed invention stands to eradicate yet another one of life's small frustrations — getting that last bit of soap out of the bottle.

Researchers at Ohio State University have designed a texture that can repel "surfactants," a name given to the class of compounds that include soap, shampoos, detergents, and similar substances.

It is another addition to a growing field of "self-cleaning" surfaces, that can repel liquids such as water or oil, and have "anti-fouling" properties that can prevent the growth of mold and bacteria. Tiny nanostructures prevent substances from gripping these surfaces, leading the mess to bead up and roll right off.

The team published its results Monday in the journal Philosophical Transactions of the Royal Society A.

The texture designed by engineers Bharat Bhushan and Philip Brown can be used to line the insides of bottles of everyday soaps and cleaning products — a kind of substance that has been particularly difficult for this kind of research. If the research produces commercially viable products, this method could considerably cut down on the amount of these chemicals that are wasted each year. It could also keep old shampoo from crusting around the lid of the bottle.

"It's what you'd call a first-world problem, right? 'I can't get all of the shampoo to come out of the bottle'," said Bhushan, a professor at Ohio State, and one of the researchers on the study, in a press release. "But manufacturers are really interested in this, because they make billions of bottles that end up in the garbage with product still in them."

Here's the mind-blowing part: the texture works because it keeps the soap from touching the inside the bottle.

Other materials can achieve a similar effect with different substances, including food containers such as ketchup bottles. But surfactants have some key characteristics that make these materials useless.

A food product like ketchup has a lot of water in it, and water molecules have high surface tension. They tend to stick to each other more than they stick to other surfaces. That is what makes water form dome-like droplets on surfaces — the molecules are all drawn to each other.

Soaps lack this trait. They have low surface tension, and they stick to surfaces more easily. Bhushan and Brown devised a new structure for their texture, using nanoparticles made out of silica.

Silica nanoparticles embedded in a piece of polycarbonate form puffy, y-shaped structures that cradle droplets of soap and prevent them from sticking to the plastic below. Researchers at The Ohio State University have made similar advances with making soap slide off of polypropylene.
Source: Philip S. Brown, Ohio State University

The structures, which look like heart-shaped corals, are spaced a few micrometers apart across the surface of the bottle. They branch out at the top, leaving a small layer of air between them and the surface of the bottle. This prevents the soap molecules from ever touching the bottle.

Bhushan told CNBC he got the idea when some people at Procter & Gamble told him they were interested in a shampoo bottle that would not let soap collect around the lid.

"I was speaking to Procter and Gamble, and I suggested self cleaning bottles — at the time I was thinking of bottles that remain free of dirt and other contaminants," Bhushan said. "And they said 'well we have been thinking about self-cleaning shampoo bottles, because the shampoo collects on the cap,' and that is how the work started. We have no relationship with them, but often I talk to people to figure out what it is we should be working on."

Bhushan told CNBC that the product potentially has many uses. He said the team was applying for a patent on Monday, and will be seeking funding for further research.

Though the product works well in their laboratory tests, they will have to work more to achieve a substance that can fully repel substances in real world situations — such as a shampoo that has been sitting in a bottle for months, as well as products that have different ingredients.

He also said the invention has potentially many applications, including in automotive parts, or even coatings to repel oils off smartphone surfaces. Bhushan said he has worked with Sony Japan and Honda, among others, on similar materials.

An email sent to Sony seeking comment was not returned at the time of publication.