'Omniphobic' coating could keep phones, homes grime free

Scientists, led by an Indian origin researcher, have developed a durable, transparent coating that repels water, oils and alcohols, paving the way for grime-proof phone screens, camera lenses and countless other everyday items.

The new "omniphobic" coating repels just about every known liquid, researchers said. It is the latest in a series of breakthrough coatings from the laboratory of Anish Tuteja, associate professor at the University of Michigan in the US.

The new coating as a way to prevent surfaces from getting grimy, both in home and industry. It could work on computer displays, tables, floors and walls, for example, Tuteja said.

"I have a 2-year-old at home, so for me, this particular project was about more than just the science," Tuteja said.

"We're excited about what this could do to make homes and daycares cleaner places, and we're looking at a variety of possible applications in industry as well," he said.

By mapping out the fundamental properties of a vast library of substances, researchers were able to mathematically predict how any two will behave when they are combined. This enabled them to concoct a nearly endless variety of combinations with very specifically tailored properties.

"In the past, researchers might have taken a very durable substance and a very repellent substance and mixed them together. But this doesn't necessarily yield a durable, repellent coating," Tuteja said.

They discovered that even more important than durability or repellency is a property called "partial miscibility," or the ability of two substances to mix together in exactly the right way.

Chemicals that play well together make a much more durable product, even if they are less durable individually.

To make a versatile coating that is optically clear and smooth enough to repel oils and alcohols, the team needed to find a repellent ingredient and a binder with exactly the right amount of miscibility, as well as the ability to stick to a wide variety of substrates. They also needed a coating that would stay smooth during processing and drying.

"You can repel water with a rough surface that creates tiny pockets of air between the water and the surface, but those surfaces don't always repel oils or alcohols because of their lower surface tension," Tuteja said.

"We needed a very smooth surface that interacts as little as possible with a variety of liquids, and we also needed ingredients that mix together very well, because too much phase separation between ingredients will scatter light," he said.

Ultimately, the team discovered that a mix of fluorinated polyurethane and a specialised fluid-repellent molecule called F-POSS would do the job.

Their recipe forms a mixture that can be sprayed, brushed, dipped or spin-coated onto a wide variety of surfaces, where it binds tightly. While the surface can be scratched by a sharp object, it is durable in everyday use.

Tuteja believes that the coating will be inexpensive by the time it sees the mass market - fluorinated polyurethane is an inexpensive, common ingredient.

While F-POSS is rare and expensive today, manufacturers are in the process of scaling it up to mass production, which should dramatically lower its cost.