How do you coax those last few drops of shampoo out of the bottle? Some people turn it upside down and let the substance collect near the lid. Some add water and shake it around. Others simply toss the bottle away when it’s almost empty, which contributes to a lot of unnecessary waste. But who can blame them? It’s a lot of pain for little gain to clean out a bottle completely.
Enter engineers Philip Brown and Bharat Hushan of Ohio State University, who’ve just developed a coating that lets soap and shampoo slide out of their plastic container with ease. To accomplish the task, Brown and Hushan looked to nature, and in particular to the lotus leaf, whose waxy coating and surface roughness both help repel water and keep leaves clean and healthy. Starting with this inspiration, the researchers had to get a bit creative.
“Nature has a limited toolbox to work with,” Brown told Digital Trends. “If we want to repel liquids like soaps and oils, we must use chemistries that nature doesn’t have access to.”
MIT engineers helped us get the last drops of ketchup from the bottle a few years ago, with a product called LiquiGlide. The shampoo task was more difficult since soaps contain surfactant molecules, which make soap feel “soapy” and help keep it clean, but which also make the substance sticky, Brown explained. “To prevent this, we must make the bottle less sticky,” he continued. “We add [chemicals] to the inside of the bottle which soap does not like to stick to. We also increase the roughness of the surface by adding nanoparticles into the plastic and this helps to enhance the effects of the non-stick [chemical].” The nanoparticles create overlaying “Y” patterns at an angle that helps the soap slide downward.
The benefits of Brown and Hushan’s coating are obvious for bathers but might also be felt outside of the bathroom. For one, the coating may help us cut down on waste as people use their soap and shampoo containers for longer. Brown also pointed out that, even when people do recycle, the leftover substances in the container can complicate recycling.
“Plastic shampoo bottles are highly recyclable,” he said. “Unfortunately, many people do not properly rinse out these containers before adding them to their recycling. The leftover product in the bottles can cause issues during recycling. With our coating, the shampoo is less likely to stick to the bottle and so the bottle is more easily recycled.”