An invention by researchers at The Ohio State University may solve one of life's recurrent annoyances: Getting that last bit of shampoo or liquid soap to reluctantly dribble out of the bottle.

Liquid soap tumbles right off the coating invented by Philip S. Brown and Bharat Bhushan, they say in a study published Sunday in the journal Philosophical Transactions of the Royal Society.

The coating also repels oils and water, the study states, and could be useful in "improving the antibacterial, mechanical and liquid-repellent properties of plastic devices."

For example, fluids could flow more freely through lab-on-a chip devices made with the coating, the study says.

However, the invention works best when the fluids are in contact with the coating for a short period of time, such as single-use applications. Work remains to be done to make it effective on products with prolonged contact, the study authors say.

Soap sliding away

The invention consists of a plastic called polypropylene with nanoparticles embedded at its surface. The surface is rough on a microscopic level, which creates tiny air pockets that prevent the soap, water or oil from sticking. The effect is strengthened by treatment with fluorosilane, which further enhances its ability to repel the liquids.

This is the first time that a polypropylene surface has been demonstrated to repellent to both water and oils at the same time, the study stated. Moreover, polypropylene is widely used for consumer packaging, automotive parts, textiles and other applications, it said.

"Water- and oil-repellent PP surfaces are therefore of interest for a wide range of industrial and consumer applications such as in packaging, where it is desirable for the product to be repelled from and not foul the container, reducing wastage and improving the customer experience."

The invention functions best when the liquid is in contact with the surface for a short time, the study said. Prolonged contact decreases its effectiveness. So it could now be used best for bottle caps or single-use products.

"However, more work is required to fully achieve shampoo repellency for PP surfaces in constant contact with shampoo such as the inside of a typical consumer bottle," the study stated.