For far too long, the blackest black paint has captivated 99.9% of public attention. Now is the time to illuminate the opposite end of the experimental paint spectrum: a new colorant dubbed “the whitest white.” Like its dark version, the fresh paint offers a wide range of possible applications, including thermal camouflage. Its coatings reflect 98.1 percent of sunlight, providing a substantial cooling effect without the need for electricity that commercial air conditioners demand.
The 98.1 percent indicates that we now absorb just 1.9 percent of sunlight, compared to 10 to 20% absorption from commercial paints that are white or “heat reflecting.” Xiulin Ruan, a mechanical engineer at Purdue University and co-author of recent research explaining the color that was published in ACS Applied Materials & Interfaces, adds, “That’s a big reduction.” The new combination can release heat from a coated structure by reflecting so much sunlight.
Ruan and his Purdue colleagues estimate that applying their paint to a 1,000-square-foot (more than 90-square-meter) roof might reduce building cooling by around 10 kilowatts. This impact may not altogether remove the need for energy-intensive air conditioners, but it may help cut down on their use. “Our model suggests that in the summer if you live in Reno, Nevada, or Phoenix, Arizona, you may save up to 70% to 80% on air conditioning,” Ruan explains.
For decades, scientists have been producing reflective paints, but today’s commercial goods are still at or above the ambient temperature. However, in the last ten years, researchers have had more success with multilayered coatings that include microscopic particles—some on the nanoscale—that reflect a wide range of light wavelengths. Stanford University and the University of Colorado Boulder have demonstrated that such materials can chill a surface to temperatures below ambient. Unfortunately, creating and applying such coatings to a character may be more expensive—and involves a more time-consuming process—than just slapping on some paint.
Ruan decided to try a hybrid approach in 2014, developing a paint that could be readily brushed or sprayed onto a surface while still containing a reflective nanomaterial. Last year, his team experimented with titanium dioxide and calcium carbonate materials and created a more fabulous yet less thoughtful paint from the latter. The researchers eventually settled on barium sulfate, a reasonably affordable chemical. Then they calculated the amount of white material needed to make the paint as reflective as possible without compromising its adhesion. Finally, the scientists ensured that the barium sulfate particles were available in various sizes, as each size scatters light at a particular wavelength.
“This research appeals to me. I believe it’s promising,” says Yuan Yang, a Columbia University materials expert who was not involved in the study. “I also believe it has the potential to be commercialized.” In a year or two, Ruan aims to bring a version of his paint to market. He points out that the price is equivalent to, or perhaps slightly cheaper than titanium dioxide used in commercial paints. “No pricey nanotechnology is used in manufacturing. Although it is still nanotechnology, it is highly cost-effective nanotechnology.”
However, there is a lot of rivalry from other scientists. Yang also points out that any reflective product must withstand the actual world, where filth accumulates overtime on surfaces. He claims that a producer will have to figure out “how to keep the painted white after 30 years of usage.”
Ruan sees his job as a means of combating the climate crisis. He believes that President [Joe] Biden talked about decreasing carbon emissions in half by 2030. “Our paint can help us achieve that aim since it allows us to cool without using electricity.”