In an effort to curb global warming, engineers at Purdue University have created the whitest paint to date. Coating buildings with this paint may one day cool them down enough to reduce the need for air conditioning, the researchers say.
In October, the team created an ultra-white paint that pushed the boundaries of white paint. Now, they’ve surpassed that. The new paint is not only whiter, but can also keep surfaces cooler than the formulation researchers previously demonstrated.
“If you used this paint to cover a roof area of about 1,000 square feet, we estimate that you could get 10 kilowatts of cooling power. It’s more powerful than the central air conditioners used by most homes, ”said Xiulin Ruan, a Purdue professor of mechanical engineering.
Researchers believe this white may be the closest equivalent to the blackest black, “Vantablack,” which absorbs up to 99.9% of visible light. The whitest new paint formulation reflects up to 98.1% of the sunlight – compared to 95.5% of the sunlight reflected by the researchers’ previous ultra-white paint – and sends infrared heat far away. ‘a surface at the same time.
Typical commercial white paint gets warmer than cooler. Paints on the market designed to reject heat reflect only 80% to 90% of sunlight and cannot make surfaces cooler than their surroundings.
The team’s research paper showing how paint works is published Thursday, April 15 on the cover of ACS Applied Materials & Interfaces.
What makes the whitest paint so white
Two characteristics give the paint its extreme whiteness. One is the very high concentration in the paint of a chemical compound called barium sulfate which is also used to make photo paper and cosmetics white.
“We looked at various commercial products, basically anything white,” 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. “We’ve found that with barium sulfate, you can theoretically make things really, really reflective, which means they’re really, really white.”
The second feature is that the barium sulfate particles are all different sizes in the paint. The amount of light scattered by each particle depends on its size, so a wider range of particle sizes allows the paint to diffuse more of the light spectrum from the sun.
“A high concentration of particles that are also different sizes gives the paint the widest spectral scattering, which contributes to the highest reflectance,” said Joseph Peoples, Ph.D. Purdue. mechanical engineering student.
There is a bit of room to make the paint whiter, but not much without compromising the paint.
“Although a higher particle concentration is better to make 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,” Li said.
How the whitest paint is also the coolest
The whiteness of the paint also means that the paint is the freshest on record. Using high-precision temperature reading equipment called thermocouples, researchers demonstrated outdoors that paint can keep surfaces 19 degrees Fahrenheit cooler than their ambient environment at night. It can also cool surfaces to 8 degrees Fahrenheit under their surroundings under strong sunlight during midday hours.
The paint’s solar reflectance is so effective that it even worked in the dead of winter. When tested outdoors with an ambient temperature of 43 degrees Fahrenheit, the paint still managed to lower the temperature of the sample by 18 degrees Fahrenheit.
This white paint is the result of six years of research building on attempts dating back to the 1970s to develop radiative cooling paint as a possible alternative to traditional air conditioners.
Ruan’s lab had looked at over 100 different materials, narrowed them down to 10, and tested about 50 different formulations for each material. Their previous whitest paint was a formulation of calcium carbonate, an earth-abundant compound commonly found in rocks and seashells.
The researchers showed in their study that, like commercial paint, their barium sulfate-based paint can potentially withstand outdoor conditions. The technique used by researchers to create the paint is also compatible with the commercial paint manufacturing process.
Patent applications for this paint formulation have been filed with the Technology Commercialization Office of the Purdue Research Foundation. This research was supported by the Cooling Technologies Research Center at Purdue University and the Air Force Office of Scientific Research through the University of Research Instrumentation Program. la Défense (grant n ° 427 FA9550-17-1-0368). The research was conducted at Purdue’s FLEX Lab and Ray W. Herrick Laboratories and the Birck Nanotechnology Center at Purdue Discovery Park.
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Material provided by Purdue University. Original written by Kayla Wiles. Note: Content can be changed for style and length.