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The whitest paint in the world now thinner than ever, ideal for vehicles

The whitest paint in the world – seen in this year’s edition of Guinness World Records and “The Late Show With Stephen Colbert” – keeps surfaces so cool they might reduce the need for air conditioning. Now, the Purdue University researchers who created the paint have developed a new thinner, lighter formulation that’s ideal for drawing heat away from cars, trains and planes.

“I’ve been contacted by everyone from spacecraft manufacturers to architects to companies that make clothes and shoes,” said Xiulin Ruan, professor of mechanical engineering at Purdue. and paint developer. “They mainly had two questions: where can I buy it and can you make it thinner?”

The original world’s whitest paint used barium sulfate nanoparticles to reflect 98.1% of sunlight, cooling exterior surfaces more than 4.5°C below ambient temperature. Cover your roof with this paint and you can essentially cool your home with a lot less air conditioning. But there is a problem.

“To achieve this level of radiative cooling below room temperature, we had to apply a layer of paint that was at least 400 microns thick,” Ruan said. “It’s perfect if you’re painting a sturdy fixed structure, like the roof of a building. But in applications that have precise size and weight requirements, the paint must be thinner and lighter.

Researchers at Purdue University have created a new formula for the world’s whitest paint, making it thinner and lighter. The previous iteration (left) required a layer 0.4 millimeters thick to achieve subambient radiation cooling. The new formulation can achieve similar cooling with a layer just 0.15 millimeters thick. It is thin and light enough for its radiant cooling effects to be applied to vehicles such as cars, trains and planes. (Photo Purdue University/Andrea Felicelli) Download image

That’s why Ruan’s team began experimenting with other materials, pushing the limit of the materials’ ability to scatter sunlight. Their latest formulation is a nanoporous paint incorporating hexagonal boron nitride as a pigment, a substance primarily used in lubricants. This new paint achieves almost the same solar reflectance benchmark (97.9%) with a single coat of 150 micron paint.

Their research has been published in Cell Reports Physical Science.

“Hexagonal boron nitride has a high index of refraction, which causes sunlight to scatter strongly,” said Andrea Felicelli, a Purdue mechanical engineering doctoral student who worked on the project. “The particles of this material also have a unique morphology, which we call nanoplatelets.”

Ioanna Katsamba, another mechanical engineering PhD student at Purdue, performed computer simulations to understand whether nanoplatelet morphology provides benefits. “The models showed us that the nanoplatelets are more effective at bouncing solar radiation than the spherical nanoparticles used in previous cooling paints,” Katsamba said.

The paint also incorporates air voids, making it highly porous at the nanoscale. This lower density, combined with the thinness, offers another huge advantage: reduced weight. The new paint weighs 80% less than barium sulfate paint, but achieves almost identical solar reflectance.

“This light weight opens the doors to all sorts of applications,” said George Chiu, Purdue mechanical engineering professor and inkjet printing expert. “Now this paint has the potential to cool the exterior of planes, cars or trains. A plane sitting on the tarmac on a hot summer day won’t have to run its air conditioning as hard to cool the interior, thus saving large amounts of energy.Spacecraft should also be as light as possible, and this painting can be one of them.

As for that other big question – where can I buy the paint? – explains Ruan. “We are currently in discussions to bring it to market,” he said. “There are still a few issues to resolve, but progress is being made.”

Either way, these Purdue researchers are eagerly awaiting what the paint might accomplish. “Using this paint will help cool surfaces and greatly reduce the need for air conditioning,” Ruan said. “This not only saves money, but also reduces energy consumption, which reduces greenhouse gas emissions. And unlike other cooling methods, this paint radiates all the heat out into deep space, which also directly cools our planet. It’s pretty amazing that a painting can do all that.

Patent applications for this paint formulation have been filed with the Technology Commercialization Office of the Purdue Research Foundation. For more details on this intellectual property, contact Will Buchanan at [email protected] and reference code 2022-RUAN-69542. This research was supported by the National Science Foundation with award No. 2102645, and Andrea Felicelli was supported by a National Science Foundation Senior Research Fellowship. The research was performed at Purdue’s FLEX Lab and Ray W. Herrick Laboratories and the Birck Nanotechnology Center in the Discovery Park District at Purdue.

About Purdue University

Purdue University is a leading public research institution that develops practical solutions to today’s toughest challenges. Ranked in each of the past five years as one of the 10 most innovative universities in the United States by US News & World Report, Purdue delivers groundbreaking research and breakthrough discoveries. Committed to hands-on, online, real-world learning, Purdue provides transformative education for all. Committed to affordability and accessibility, Purdue has frozen tuition and most fees at 2012-13 levels, allowing more students than ever to graduate debt-free. Learn how Purdue never stops in the persistent pursuit of the next giant leap at

About the Purdue Research Foundation Office of Technology Commercialization

The Purdue Research Foundation’s Office of Technology Commercialization operates one of the most comprehensive technology transfer programs among leading research universities in the United States. The services provided by this office support Purdue University’s economic development initiatives and benefit the university’s academic activities through Purdue’s marketing, licensing and protection. intellectual property. The office is located in the Convergence Center for Innovation and Collaboration in the Discovery Park District at Purdue, adjacent to the Purdue campus. In fiscal year 2021, the bureau reported 159 agreements finalized with 236 technologies signed, 394 disclosures received, and 187 U.S. patents granted. The office is managed by the Purdue Research Foundation, which received the 2019 Innovation and Economic Prosperity Universities Award for Place from the Association of Public and Land-grant Universities. In 2020, IPWatchdog Institute ranked Purdue third nationally for startup creation and in the top 20 for patents. The Purdue Research Foundation is a private, nonprofit foundation established to advance the mission of Purdue University. Contact [email protected] for more information.

Media contact: Kayla Wiles, 765-494-2432, [email protected]

Writer: Jared Pike

Source: Xiulin Ruan, [email protected]

Lightweight, Ultrawhite Hexagonal Boron Nitride Nanoporous Thin Film Paints for Daytime Radiative Cooling

Physical Sciences Cell Reports

DOI: 10.1016/j.xcrp.2022.101058

The abstract and list of authors are available online.

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