This year’s Guinness World Records list as well as “The Late Show with Stephen Colbert” featured the world’s whitest paint, which can keep surfaces so cool that it could lessen the need for air conditioning.
The Purdue University researchers that invented the paint have designed a new mix that is lighter and thinner and is perfect for dispersing heat away from vehicles like cars, trains, and airplanes.
I have been contacted by everyone from spacecraft manufacturers to architects to companies that make clothes and shoes. They mostly had two questions: Where can I buy it, and can you make it thinner?
Xiulin Ruan, Professor, Mechanical Engineer, Purdue University
The first world’s whitest paint employed barium sulfate nanoparticles to reflect 98.1% of sunlight, lowering the temperature of outdoor surfaces by more than 4.5 °C. That paint will essentially cool homes with significantly less air conditioning if the roof is coated in it. However, there is an issue.
Ruan stated, “To achieve this level of radiative cooling below the ambient temperature, we had to apply a layer of paint at least 400 microns thick. That is fine if you are 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.”
Ruan’s team started experimenting with different materials to stretch their limits regarding how much light they could scatter. Their most recent innovation is a nanoporous paint that uses the pigment hexagonal boron nitride, which is typically found in lubricants.
With just one 150-micron coat of paint, this new paint achieves virtually the same threshold of solar reflectance (97.9%).
Cell Reports Physical Science published their research.
Hexagonal boron nitride has a high refractive index, which leads to strong scattering of sunlight. The particles of this material also have a unique morphology, which we call nanoplatelets.
Andrea Felicelli, PhD Student, Mechanical Engineering, Purdue University
To determine whether the nanoplatelet morphology has any advantages, Ioanna Katsamba performed computer simulations.
Katsamba, another PhD student in mechanical engineering at Purdue, stated, “The models showed us that the nanoplatelets are more effective in bouncing back the solar radiation than spherical nanoparticles used in previous cooling paints.”
Additionally, the paint has air gaps that give it a high nanoscale porosity. Along with being thinner, this lower density offers a significant weight reduction. The newer paint provides approximately equal solar reflectance while weighing 80% less than barium sulfate paint.
George Chiu, a Purdue Professor of Mechanical Engineering and an expert in inkjet printing, stated, “This lightweight opens the doors to all kinds of applications. 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.”
Ruan responds to the other important query, “Where can I acquire the paint?”
“We are in discussions right now to commercialize it. There are still a few issues that need to be addressed, but progress is being made,” Ruan added.
In either case, the Purdue scientists are eager to see what the paint can do.
Ruan further stated, “Using this paint will help cool surfaces and greatly reduce the need for air conditioning. This not only saves money, but it reduces energy usage, which in turn reduces greenhouse gas emissions.”
He added, “And unlike other cooling methods, this paint radiates all the heat into deep space, which also directly cools down our planet. It is pretty amazing that a paint can do all that.”
The Purdue Research Foundation Office of Technology Commercialization has submitted patent applications for this paint composition. For further information on this intellectual property, contact Will Buchanan ([email protected]) and include the reference code 2022-RUAN-69542.
The National Science Foundation provided funding for this study under Award No. 2102645, and a Graduate Research Fellowship from the NSF was provided to Andrea Felicelli. Purdue’s FLEX Lab, Ray W. Herrick Laboratories, and Birck Nanotechnology Center of Discovery Park District were used for the research.
Felicelli, A., et al. (2022) Thin layer lightweight and ultrawhite hexagonal boron nitride nanoporous paints for daytime radiative cooling. Cell Reports Physical Science. doi:10.1016/j.xcrp.2022.101058