In an effort to curb global warming, Purdue University engineers have created the whitest paint yet. Coating buildings with this paint may one day cool them off enough to reduce the need for air conditioning, the researchers say.
In October 2020, the team created an ultra-white paint that pushed limits on how white paint can be. In April 2021, they’ve outdone that. The newer paint not only is whiter — it’s the whitest paint ever and has earned a Guinness World Records title for it — but also can keep surfaces cooler than the formulation that the researchers had previously demonstrated.
“If you were to use this paint to cover a roof area of about 1,000 square feet, we estimate that you could get a cooling power of 10 kilowatts. That’s more powerful than the central air conditioners used by most houses,” said Xiulin Ruan, a Purdue professor of mechanical engineering.
The researchers believe that this white may be the closest equivalent of the blackest black, “Vantablack,” which absorbs up to 99.9% of visible light. The new whitest paint formulation reflects up to 98.1% of sunlight — compared with the 95.5% of sunlight reflected by the researchers’ previous ultra-white paint — and sends infrared heat away from a surface at the same time.
In contrast, typical commercial white paint gets warmer rather than cooler. Paints on the market that are designed to reject heat reflect only 80%-90% of sunlight and can’t make surfaces cooler than their surroundings.
Two features give the paint its extreme whiteness. One is the paint’s very high concentration of a chemical compound called barium sulfate, which is also used to make photo paper and cosmetics white.
The second feature is that the barium sulfate particles are all different sizes in the paint. How much each particle scatters light depends on its size, so a wider range of particle sizes allows the paint to scatter more of the light spectrum from the sun.
“A high concentration of particles that are also different sizes gives the paint the broadest spectral scattering, which contributes to the highest reflectance,” said Joseph Peoples, a Purdue Ph.D. student in mechanical engineering.
There is a little bit of room to make the paint whiter, but not much without compromising the paint.
“Although a higher particle concentration is better for making something white, you can’t increase the concentration too much. The higher the concentration, the easier it is for the paint to break or peel off,” said Xiangyu Li, a postdoctoral researcher at the Massachusetts Institute of Technology, who worked on this project as a Purdue Ph.D. student in Ruan’s lab.
The paint’s whiteness also means that the paint is the coolest on record. Using high-accuracy temperature reading equipment called thermocouples, the researchers demonstrated outdoors that the paint can keep surfaces 19 degrees Fahrenheit cooler than their ambient surroundings at night. It can also cool surfaces 8 degrees Fahrenheit below their surroundings under strong sunlight during noon hours.
This white paint is the result of six years of research building on attempts going back to the 1970s to develop radiative cooling paint as a feasible alternative to traditional air conditioners.
Ruan’s lab had considered over 100 different materials, narrowed them down to 10 and tested about 50 different formulations for each material. The technique that the researchers used to create the paint also is compatible with the commercial paint fabrication process.
The researchers have partnered with a company to scale up the paint and put it on the market. Patent applications for this paint formulation have been filed through the Purdue Research Foundation Office of Technology Commercialization.
This research was supported by the Cooling Technologies Research Center at Purdue University and the Air Force Office of Scientific Research through the Defense University Research Instrumentation Program. The research was performed at Purdue’s FLEX Lab and Ray W. Herrick Laboratories and the Birck Nanotechnology Center of Purdue’s Discovery Park.
Using this paint formulation to cover a roof area of about 1,000 square feet could result in a cooling power of 10 kilowatts, which is more powerful than the air conditioners used by most houses.
Two features make this paint ultra-white: a very high concentration of a chemical compound called barium sulfate — also used in photo paper and cosmetics — and different particle sizes of barium sulfate in the paint. What wavelength of sunlight each particle scatters depends on its size, so a wider range of particle sizes allows the paint to scatter more of the light spectrum from the sun.
It would be interesting to see which municipality will be the first to adopt Purdue's super-white paint to cool off its buildings. Indianapolis and Chicago may be the biggest nearby cities but there are warmer cities that could benefit much more from the world's whitest paint. But who knows, perhaps they opt to procure this paint anyway - to low down their cooling bills during the summer, while at the same time showing their municipalities are willing to adopt novel materials and technologies. Needless to say, you could lead such an effort and score some political points along the way.
If your business sell construction materials or is in any other way involved in the construction industry, perhaps you could contact the Purdue Research Foundation Office of Technology Commercialization and explore the ways how your company could be involved in (re)selling their super-white paint. From what we can tell, such a product offers nothing but benefits, especially in warm areas where air cooling costs can easily go through the roof. Heck, even in cities with only warm summers — and there's a growing number of these — Purdue's paint will "do the trick." It's up to you to grab this opportunity and make money out of it.