Our phones follow us everywhere – which often puts them in the line of fire for spilt drinks or rain. But now a team at the University of Michigan has developed a durable, clear coating that could help phones – or any surface, for that matter – repel almost any liquid.
Over the years, the Michigan team, led by Anish Tuteja, has developed a wide range of liquid-repelling coatings, including self-healing superhydrophobic materials, rubbery ice-shedding coatings and a superomniphobic coating that could reportedly resist basically any liquid.
Building on those years of previous research, the team set out to make a new omniphobic coating that was more durable than past iterations, and was clear enough to be used on touchscreens, displays and windows. Balancing these three key properties – strength, transparency and repellency – was a challenge, but the team found that the most important factor was choosing ingredients that mixed together in just the right way.
"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," says Tuteja. "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."
Instead of a trial-and-error method, the team used algorithms on a large library of chemicals to predict how they'd behave when mixed together. Eventually they found that the ideal recipe included fluorinated polyurethane and a molecule named F-POSS, which is great at repelling fluids.
"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," says Mathew Boban, an author on the paper. "That separation allows the F-POSS to sort of float to the surface and create a nice repellent layer."
The coating can be sprayed, brushed, dipped or spin-coated onto a range of surface types, and once it dries it forms a durable, clear layer that's tightly bound to the underlying surface. While the fluorinated polyurethane is common and cheap already, F-POSS is harder to come by, but the researchers say that other work is looking into how to mass produce the molecules, which should result in an inexpensive coating.
If it does make it to market, the team says the omniphobic coating could be used in phone and computer displays, camera lenses, countertops and tables, floors, walls, windows, and almost anywhere else that might need protection from liquids. More creative uses might include improving the efficiency of refrigeration, oil refining equipment and anything else that works through condensation.
Before it gets used this widely though, the researchers are conducting further work to ensure that the coating is non-toxic.
The research was published in the journal ACM Applied Materials & Interfaces, and the coating is demonstrated in the video below.
Source: University of Michigan