SNOW WHITE AND THE BARIUM SULFATE DWARFS

“SCIENTISTS AT PURDUE,” reports Cara Buckley in The New York Times, July 12, 2023, “have created a white paint that, when applied, can reduce the surface temperature on a roof and cool the building beneath it.”

Buckley writes, “The paint’s properties are almost superheroic. It can make surfaces as much as eight degrees Fahrenheit cooler than ambient air temperatures at midday, and up to 19 degrees cooler at night, reducing temperatures inside buildings and decreasing air-conditioning needs by as much as 40 percent. It is cool to the touch, even under a blazing sun, Dr. Ruan said. Unlike air-conditioners, the paint doesn’t need any energy to work, and it doesn’t warm the outside air.” 

Xiulin Ruan, Purdue mechanical engineering prof, and his students have created a white paint that reflects 98 percent of sunlight. Image by John Underwood/Purdue University from The New York Times. 

Barium Sulfate Nanoparticles. As described in an earlier Purdue University news release, October 3, 2022, “The original world’s whitest paint used nanoparticles of barium sulfate to reflect 98.1% of sunlight, cooling outdoor surfaces more than 4.5°C below ambient temperature. Cover your roof in that paint, and you could essentially cool your home with much less air conditioning.”

Barium sulfate makes things like photo paper and cosmetics very reflective. The Purdue news release notes the importance of its nanoparticle distribution:  “… 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.”

Dr. Ruan, left, and grad student Joseph Peoples use an infrared camera to compare two panels of different white paint. Image by Jared Pike/Purdue University from The New York Times.

Another Approach. Back in 2018, SimanaitisSays offered “Talking About Paint That’s Cool.” An approach developed by researchers at Columbia University was similar to barium sulfate nanoparticles: Robert F. Service described PVDF-HFP (Polyvinylidene fluoride-co-hexafluoropropylene) in Science, September 28, 2018: “The polymer starts as a solution in acetone, to which the researchers add a small amount of water. When painted on a surface, the acetone quickly evaporates, and the polymer separates from the water, creating a network of water droplets. Finally, the water also evaporates, leaving a spongelike arrangement of interconnected voids that reflect up to 99.6% of light, including IR, visible, and UV. The dried film also emits heat primarily in the desirable mid-IR range.”

Images from Science, September 28, 2018.

Not Without Tradeoffs. “Though durable,” Service noted, “PVDF-HFP is roughly five times as expensive as traditional acrylics used in paints.”

And, in the larger climate-change challenge, Cara Buckley writes, “Geoengineering—manipulating different processes to control the Earth’s climate—has also been criticized for distracting from the root problem: Humans must stop burning fossil fuels to avoid more catastrophic effects of climate change.” One of her sources tells her, “This is definitely not a long-term solution to the climate problem. This is something you can do short term to mitigate worse problems while trying to get everything under control.” ds 

© Dennis Simanaitis, SimanaitisSays.com, 2023