The world's whitest paint -- seen in this year's edition of Guinness World Records and "The Late Show With Stephen Colbert" -- keeps surfaces so cool that it could reduce the need for air conditioning. Now the Purdue University researchers who created the paint have developed a new formulation that is thinner and lighter -- ideal for radiating heat away from cars, trains and airplanes.
From: Purdue University
October 3, 2022 -- "I've
been contacted by everyone from spacecraft manufacturers to architects to
companies that make clothes and shoes," said Xiulin Ruan, a Purdue
professor of mechanical engineering and developer of the paint. "They
mostly had two questions: Where can I buy it, and can you make it thinner?"
The original world's
whitest paint used nanoparticles of barium sulfate to reflect 98.1% of
sunlight, cooling outdoor surfaces more than 4.5°C below ambient temperature.
Cover your roof in that paint, and you could essentially cool your home with
much less air conditioning. But there's a problem.
"To achieve this
level of radiative cooling below the ambient temperature, we had to apply a
layer of paint at least 400 microns thick," Ruan said. "That's fine
if you're painting a robust stationary structure, like the roof of a building.
But in applications that have precise size and weight requirements, the paint
needs to be thinner and lighter."
That's why Ruan's team
began experimenting with other materials, pushing the limit of materials'
capability to scatter sunlight. Their latest formulation is a nanoporous paint
incorporating hexagonal boron nitride as the pigment, a substance mostly used
in lubricants. This new paint achieves nearly the same benchmark of solar
reflectance (97.9%) with just a single 150-micron layer of paint.
Their research has been
published in Cell Reports Physical Science.
"Hexagonal boron
nitride has a high refractive index, which leads to strong scattering of
sunlight," said Andrea Felicelli, a Purdue PhD student in mechanical
engineering who worked on the project. "The particles of this material
also have a unique morphology, which we call nanoplatelets."
Ioanna Katsamba,
another PhD student in mechanical engineering at Purdue, ran computer
simulations to understand if the nanoplatelet morphology offers any benefits.
"The models showed us that the nanoplatelets are more effective in
bouncing back the solar radiation than spherical nanoparticles used in previous
cooling paints," Katsamba said.
The paint also
incorporates voids of air, which make it highly porous on a nanoscale. This
lower density, together with the thinness, provides another huge benefit:
reduced weight. The newer paint weighs 80% less than barium sulfate paint yet
achieves nearly identical solar reflectance.
"This light weight
opens the doors to all kinds of applications," said George Chiu, a Purdue
professor of mechanical engineering and an expert in inkjet printing. "Now
this paint has the potential to cool the exteriors of airplanes, cars or
trains. An airplane sitting on the tarmac on a hot summer day won't have to run
its air conditioning as hard to cool the inside, saving large amounts of
energy. Spacecraft also have to be as light as possible, and this paint can be
a part of that."
As to that other big
question -- where can I buy the paint? -- Ruan explains. "We are in
discussions right now to commercialize it," he said. "There are still
a few issues that need to be addressed, but progress is being made."
Either way, these
Purdue researchers look forward to what the paint could accomplish. "Using
this paint will help cool surfaces and greatly reduce the need for air
conditioning," Ruan said. "This not only saves money, but it reduces
energy usage, which in turn reduces greenhouse gas emissions. And unlike other
cooling methods, this paint radiates all the heat into deep space, which also
directly cools down our planet. It's pretty amazing that a paint can do all
that."
https://www.sciencedaily.com/releases/2022/10/221003152158.htm
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