American Society for Microbiology researchers have come up with a new method that can create the perfect texture inside plastic bottles to let soap products flow freely.
The technique involves lining a plastic bottle with microscopic y-shaped structures that cradle the droplets of soap aloft above tiny air pockets, so that the soap never actually touches the inside of the bottle.
The y structures are built up using much smaller nanoparticles made of silica, or quartz, an ingredient in glass--which, when treated further, won't stick to soap.
Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor of mechanical engineering at Ohio State said compared to soaps, getting ketchup out of a bottle is trivial. The coating repels liquids in general, but getting it to repel soap was the hard part.
Engineers Bharat Bhushan and Philip Brown Bhushan came up with a method to spray-coat a small amount of solvent and ultra-fine silica nanoparticles onto the inside of bottles.
The structures are only a few micrometers, millionths of a meter high, and covered in even smaller branchlike projections. They look like shaggy heart-shaped pillows, but they're hard as glass.
Researchers found that they don't cover the inside of the bottle completely, either, but instead are planted a few micrometers apart. The main branches of the y overhang the plastic surface at an angle less than 90 degrees--steep enough that water, oils and even surfactant can't physically sustain a droplet shape that would fall in between the branches and touch the plastic.
We all struggle with shampoo bottles at home, Bhushan said. I have a few in my shower right now. Trying to get the last drop out, I put it upside down, and my wife adds water to the bottle and fights with it for a while, and then we give up and just throw it away.
With further development, the university hopes to license the coating technique to manufacturers, not just for shampoo bottles, but for other plastic products that have to stay clean, such as biomedical devices or catheters.
They have already applied the same technique to polycarbonate, a plastic used in car headlights and smartphone cases, among other applications.
The study is published in journal Philosophical Transactions of the Royal Society A.
