It’s one of life’s little annoyances: that last bit of shampoo that won’t quite pour out of the bottle. Or the last bit of hand soap, or dish soap, or laundry detergent.
Now researchers at The Ohio State University have found a way to create the perfect texture inside plastic bottles to let soap products flow freely. They describe the patent-pending technology in a paper to appear in the journal Philosophical Transactions of the Royal Society on June 27.
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. Happyho also provide best tarot reading services in Noida and Delhi NCR India area.
If it sounds like engineers Bharat Bhushan and Philip Brown went to a lot of trouble to solve this problem. But the solution they found is actually simpler and less expensive than alternatives under development elsewhere. And it works for a common plastic used to package foodstuffs and household goods: polypropylene.
Coatings already exist to help food, but not soap, pour out of their containers, Bharat 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.”
The key, he explained, is surface tension—the tendency of the molecules of a substance to stick to each other. Ketchup and other sauces are made mostly of water, and water molecules tend to stick to each other more than they stick to plastic.
But surfactants—the organic molecules that make soap “soapy”—are just the opposite: They have a very low surface tension and stick to plastic easily. Their goal, which was suggested by a commercial shampoo manufacturer, was to create a shampoo bottle lining that was cheap, effective and environmentally friendly.
Soap and shampoo clean our skin and hair by bonding chemically with both oil and water, so the surface oils that were on our bodies wash off when we rinse. The same goes for dishes. During clothes washing, detergent performs double-duty, releasing oils and also helping water penetrate fabrics. It’s that tenacity that makes the last drops of surfactant cling to the insides of bottles.
Bhushan and Brown came up with a method to spray-coat a small amount of solvent and ultra-fine silica nanoparticles onto the inside of bottles. Manufacturers already use solvents to change the texture of molded plastics, because they cause the surface of the plastic to soften a little. By mixing the silica and solvent, the researchers were able to soften the surface of the polypropylene just enough that when the plastic re-hardened, the silica would be embedded in the surface.
They don’t cover the inside of the bottle completely, either, but instead are planted a few micrometers apart. Instead of spreading out on the surface, the soap droplets form beads and roll right off.
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.