Engineers at The Ohio State University have developed a surface material that allows shampoos and soaps to glide almost effortlessly out of their plastic containers.

Developed at the suggestion of a commercial shampoo manufacturer, the bottle lining is said to be inexpensive, effective and environmentally friendly.

Engineers have invented a coating to help soap pour more easily from plastic bottles. Source: Philip S. Brown, The Ohio State UniversityAs explained by researchers, the technique involves lining a plastic bottle, in this case polypropylene, 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, the same as for glass, which, when treated further, won't stick to soap.

What makes soaps so sticky, unlike other liquid substances, are surfactants, the organic compounds that make soap “soapy.” They have a low surface tension and stick easily to plastic. The challenge was to create a surface material that could repel tenacious surfactants.

University engineers devised a method to spray-coat a small amount of solvent and ultra-fine silica nanoparticles on the inside of a plastic bottle. Mixing the silica and solvent, researchers were able to soften the surface of the polypropylene bottle just enough so that when the plastic re-hardened, the silica would be embedded in the surface.

The end result, as shown in this video, was a new type of surface material that forms invisible air pockets causing soap droplets to bead up and glide easily down a plastic surface.

With further development, the university hopes to license the coating technique to manufacturers, not only for shampoo and soap bottles, but for other plastic products that have to stay clean, such as biomedical devices or catheters.