University of Michigan
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| Yes, we used this graphic before. Couldn't resist an encore |
On your car windshield, ice is a nuisance.
But on an airplane, a wind turbine, an oil rig or power line, it can be downright dangerous.
And removing it with the methods that are available today--usually chemical melting agents or labor-intensive scrapers and hammers--is difficult and expensive work.
That could soon change thanks to a durable, inexpensive
ice-repellent coating developed by University of Michigan researchers.
Thin,
clear and slightly rubbery to the touch, the spray-on formula could make ice
slide off equipment, airplanes and car windshields with only the force of
gravity or a gentle breeze.
This could have major implications in industries
like energy, shipping and transportation, where ice is a constant problem in
cold climates.
The new coating could also lead to big energy savings in
freezers, which today rely on complex and energy-hungry defrosting systems to
stay frost-free.
An ice-repelling coating could do the same job with zero
energy consumption, making household and industrial freezers up to 20 percent
more efficient. The coating is detailed in a new paper published in the journal Science
Advances.
Made of a blend of common synthetic rubbers, the formula marks a departure from earlier approaches that relied on making surfaces either very water-repellent or very slippery.
"Researchers had been trying for years to dial down ice
adhesion strength with chemistry, making more and more water-repellent
surfaces," said Kevin Golovin, a doctoral student in materials science and
engineering. "We've discovered a new knob to turn, using physics to change
the mechanics of how ice breaks free from a surface."
Led by Anish Tuteja, associate professor of materials science
and engineering, the team initially experimented with water-repelling surfaces
as well, but found that they weren't effective at shedding ice.
But during
their experiments, they noticed something unexpected: rubbery coatings worked
best for repelling ice, even when they weren't water-repellent.
Eventually, they
discovered that the ability to shed water wasn't important at all. The rubbery
coatings repelled ice because of a different phenomenon, called
"interfacial cavitation."
Golovin explains that two rigid surfaces--say, ice and your car
windshield--can stick tightly together, requiring a great deal of force to
break the bond between them.
But because of interfacial cavitation, a solid
material stuck to a rubbery surface behaves differently. Even a small amount of
force can deform the rubbery surface, breaking the solid free.
"Nobody had explored the idea that rubberiness can reduce
ice adhesion," Tuteja said. "Ice is frozen water, so people assumed
that ice-repelling surfaces had to also repel water. That was very
limiting."
The new approach makes it possible to dramatically improve
durability compared to previous icephobic coatings, which relied on fragile
materials that lost their ice-shedding abilities after just a few freeze-thaw
cycles.
The new coatings stood up to a variety of lab tests including peel tests,
salt spray corrosion, high temperatures, mechanical abrasion and hundreds of
freeze-thaw cycles.
The team has also found that by slightly altering the smoothness
and rubberiness of the coating, they can fine-tune its degree of ice repellency
and durability. Softer surfaces tend to be more ice-repellent but less durable,
while the opposite is true for harder coatings.
Golovin believes that that
flexibility will enable them to create coatings for a huge variety of
applications.
"An airplane coating, for example, would need to be
extremely durable, but it could be less ice-repellent because of high winds and
vibration that would help push ice off," Golovin said.
"A freezer
coating, on the other hand, could be less durable, but would need to shed ice
with just the force of gravity and slight vibrations. The great thing about our
approach is that it's easy to fine-tune it for any given application."
The team has already designed hundreds of ice-repelling
formulas. Some are rough to the touch, some smooth; some shed water while
others don't.
"I think the first commercial application will be in
linings for commercial frozen food packaging, where sticking is often a
problem. We'll probably see that within the next year," Tuteja said.
"Using this technology in places like cars and airplanes will be very
complex because of the stringent durability and safety requirements, but we're
working on it."
The team received funding and assistance from the U-M MTRAC
program, created to support new innovations that demonstrate high commercial
potential. MTRAC is funded in partnership with the Michigan Economic
Development Corporation's Entrepreneur and Innovation initiative, which focuses
on establishing Michigan as the place to create and grow a business by
providing high-tech startup companies with access to a variety of resources.