Researchers at Ohio State University have created a shampoo bottle said to prevent wastage by emptying every last drop of product.
Scientists at the university lined plastic bottles with a coating formed with microscopic y-shaped structures created using nanoparticles of silica and quartz. These prevent the product inside the bottle from ever touching the edges, ensuring that it doesn’t get stuck.
The innovation is designed to work with polypropylene – a common plastic used to package household goods. Bharat Bhushan, Eminent Scholar at Ohio, explained: “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’. But manufacturers are really interested in this, because they make billions of bottle that end up in the garbage with product still in them.”
Coatings are already used to prevent food sticking in containers, but cosmetic products can be more difficult to work with. Bhushan said: “Compared to soaps, getting ketchup out of a bottle is trivial. Our coating repels liquids in general, but getting it to repel soap was the hard part.”
Surfactants have a low surface tension, which means they stick to the plastic used in shampoo bottles very easily. Philip Brown, Postdoctoral Research Scholar at Ohio State, explained: “It was an extra challenge for us to make a surface that could repel surfactant.”
The coating can be sprayed onto the inside of bottles with a solvent. This softens the surface of the polypropylene bottle enough that when the plastic re-hardens the silica nanoparticles are embedded in its surface.
Rather than forming a solid coating, the y-shaped nanoparticles are distributed several micrometers apart. The structures create 90º angles that are steep enough to prevent water, oils and even surfactant from sustaining a droplet shape and falling between the branches to touch the plastic surface. Brown explained: “You end up with air pockets underneath the surface and that;s what gives you liquid repellency.”
Ohio State believes that as well as reducing waste product, the innovation could help increase recycling rates. Bhushan explained: “We all struggle with shampoo bottles at home. I have a few in my shower right now. Trying to get that last drop out, I put it upside down and my wife adds water to the bottle and fights with it for a while. Then we just give up and throw it away.”
The researchers also believe the innovation could be used in medical applications as well, helping to keep equipment such as catheters clean. The technique has already been applied to polycarbonate, a plastic used in smartphone cases and car headlights.
