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Given that white was one of the first colors used in art in the 15th century, one would think that there is little room left to improve its "whiteness." It turns out that is far from the case. A team of researchers led by Xiulin Ruan, a professor of mechanical engineering at Indiana's Purdue University, recently revealed an "ultra-white" paint that they believe could even help combat climate change.
The scientists, who spent six years creating the world's "whitest white" paint, assert that the options currently available make surfaces warmer rather than cooler. That's because they only reflect 80 to 90 percent of the sunlight and cannot make the exterior cooler than the surrounding temperature. The newly-revealed ultra-white paint not only reflects 98.1 percent of sunlight, but also prevents surface infrared heat from being absorbed.
“We think of 90% to 98% as not very different, but we need to think about the absorption of the sunlight,” Dr. Ruan says. “Our paint absorbs 1.9% of sunlight, but those commercial paints, even with reflectants, absorb 10% of the sunlight—five times as much as our paint absorbs. They look white, they are pretty white, but they aren’t white enough—they’re not able to cool beyond the ambient temperature.”
The ultra white paint's incredible cooling ability can be attributed to the use of a high concentration of barium sulfate, in lieu of the commonly-used titanium dioxide as a pigment. The chemical compound, which can be found in cosmetics and photo paper, does not absorb UV light. The researchers also varied the size of the chemical compound's particles to allow for maximum diffusion of sunlight.
"A high concentration of particles that are also different sizes gives the paint the broadest spectral scattering, which contributes to the highest reflectance," said Purdue Ph.D. student and study participant Joseph Peoples.
Outdoor tests of the newly-formulated paint indicated it could keep surfaces 8 degrees Fahrenheit cooler than the ambient temperature under the strong noon sunlight and as much as 19 degrees Fahrenheit cooler at night. Given that the paint is as efficient in the winter — lowering surface temperatures by 18 degrees Fahrenheit when outdoor temperatures were below 43 degrees Fahrenheit — it would be most effective in areas with year-round hot weather.
"We did a very rough calculation," Dr. Ruan told the BBC. "And we estimate we would only need to paint 1 percent of the Earth's surface with this paint — perhaps an area where no people live that is covered in rocks — and that could help fight the climate change trend."
However, Hashem Akbari, professor of building, civil, and environmental engineering at Concordia University, believes the paint's real benefits can only be ascertained after being in use for a few years. “Soot and dust tend to decrease the reflectivity of the surface,” Akbari told Gizmodo.com. “If they start with super-duper 95% reflectivity, the pollutants from the air, the droplets, soot could collect on the surface, and they decrease the reflectants.”
Meanwhile, Andrew Parnell, who works on sustainable coatings at the University of Sheffield, UK, is concerned that the carbon dioxide emitted by the mining of barium sulfate may offset the lower energy outlay caused by the ultra white paint. He instead believes that green or living roofs, which are covered with vegetation, may be a more practical and effective solution to combat global warming.
The Purdue researchers, who published their study in the journal ACS Applied Materials & Interfaces on April 15, 2021, are undeterred by the skeptics. The team is not only working with manufacturers to bring the ultra white paint to market, but also developing other "energy-efficient" colors. Dr. Ruan has even hinted at creating a dynamic paint that can reflect heat in the summer and absorb it in the winter!
Resources:eurakaalert.org, gizmodo.com, bbc.com