The World’s Whitest Paint Is Also the Coolest

The World’s Whitest Paint Is Also the Coolest

Purdue University engineers are winners of the 2023 Gizmodo Science Fair for making the world’s whitest paints.

The Question

Can you increase the reflectivity of paint to keep buildings as cool as possible — and adapt that paint to use on things like cars and planes that need lighter-weight material?

The Results

In 2021, a team of engineers at Purdue University announced they had made the world’s whitest paint, which is able to reflect more than 98% of sunlight and greatly reduce the need for air conditioning in buildings. Last year, they created a lighter-weight version that could be used for planes, spacecraft, and other vehicles, which was still able to reflect 97.9% of sunlight with a very thin application of paint.

Why They Did It

“In 2021, we published the barium sulfate paint, which is still the whitest on record,” said Xiulin Ruan, a professor of mechanical engineering at Purdue and lead researcher on the project. “That’s suitable for buildings and other stationary infrastructure.”

“For large vehicles like commercial aeroplanes, the paint is not an insignificant part of their weight,” said George Chiu, a professor of mechanical engineering at Purdue whose research focuses on digital printing. “There is actually a significant cost savings associated with getting the weight down. If you can achieve the same thermal property of the paint with an 80% weight reduction, that’s a significant savings for the airline. And the weight savings translates to fuel savings, and that makes for a more sustainable transportation system as well.”

Illustration: Vicky Leta
Illustration: Vicky Leta

“We wanted to look at approaches that could improve the reflectance while also reducing the weight of the paint,” said Andrea Felicelli, a Purdue PhD student in mechanical engineering whose research focuses on nanocomposite materials.

“We wanted to see how the [platelet] shape really affects the performance of the paint,” said Ionna Katsamba, also a PhD student in mechanical engineering at Purdue, who focused on modelling the physics behind the paints. “We found that it was kind of limited in the literature, people really investigating the shapes of nanoparticles and getting the optical properties.”

Why They’re a Winner

The team took an old concept — the idea of white paint reflecting sunlight to naturally cool buildings — and combined it with nanotechnology to create some of the world’s whitest paints. The paint created in 2021 was made using high concentrations of barium sulfate, a compound that has different-sized particles to help scatter sunlight. After this success, Ruan and colleagues turned to figuring out how to create a lighter-weight version. This team ended up incorporating hexagonal boron nitride, which is used mostly in lubricants and has a unique morphology that lowers the density of the material, to reduce the paint’s thickness and weight and maintain nearly all of its reflective properties. Paints like these can keep buildings and vehicles much cooler than traditional white paints on the market, helping us adjust to hotter temperatures without using excess energy for cooling.

What’s Next

There are many potential future applications for this paint, which Ruan says they’re in discussions to commercialize. The team is working to ensure their paints can resist dirt, as well as exploring creating paint in other colours that can still reflect significant amounts of sunlight. Down the line, Ruan says he’s interested in using nanotechnology to create paint that can change colours based on the seasons, to keep buildings warm in the winter and cool in the summer.

The Team

Xiulin Ruan, professor of mechanical engineering at Purdue; George Chiu, Professor of Mechanical Engineering and Assistant Dean for Global Engineering Programs and Partnerships; Ioanna Katsamba, PhD student at Purdue; and Andrea Felicelli, PhD student at Purdue.

See the full list of Gizmodo Science Fair winners

Read more: Just How White Can White Paint Get?

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