The ‘omniphobic’ coating has been created by a team led by Anish Tuteja, U-M associate professor of materials science and engineering. It is claimed to be the first coating that is durable, clear and able to be applied to virtually any surface.
Prof Tuteja envisions 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.
“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.”
According to the researchers, the industrial uses for the coating include refrigeration, power generation and oil refining — all industries that depend on the condensation of liquids. The coating could enable equipment to slough off condensed water and chemicals more quickly, increasing efficiency by up to 20%.
Prof Tuteja says this coating is the latest result of the team’s systematic approach, which breaks with the traditional materials science ‘mix-and-see’ approach. By mapping out the fundamental properties of a vast library of substances, they’re able to mathematically predict how any two will behave when they're combined. This enables them to concoct a nearly endless variety of combinations with very specifically tailored properties.
The team discovered that even more important than durability or repellency is a property called ‘partial miscibility’ – 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’re less durable individually.
Tweaking the miscibility of this coating posed a particular challenge. To make a versatile coating that's 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.
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 variety of surfaces, where it binds tightly.
“The repellent and binder mix together well enough to make a clear coating, but there's a very small amount of phase separation between them,” said Mathew Boban, a U-M materials science and engineering graduate researcher. “That separation allows the F-POSS to sort of float to the surface and create a nice repellent layer.”
Fluorinated polyurethane is an inexpensive, common ingredient and, 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. Prof Tuteja estimates that the coating could go to market within the next two years.
The team is carrying out further studies to ensure that the coating is nontoxic.