The World's New Blackest Black and Whitest White(s): Here we go again, again
On September 12th of 2019, engineers at MIT announced that they have achieved the unimaginable — they’ve managed to beat Vantablack, formally the blackest black ever created, by inventing one that’s roughly ten times blacker.
“The material is made from vertically aligned carbon nanotubes, or CNTs — microscopic filaments of carbon, like a fuzzy forest of tiny trees, that the team grew on a surface of chlorine-etched aluminum foil,” writes Jennifer Chu for MIT News. The foil captures at least 99.995% of any incoming light, which is a big deal, since “scientists believe that forests of carbon nanotubes can trap and convert most incoming light to heat.”
One year later, on October 21st of 2020, engineers at Purdue University announced the arrival of the world’s whitest white — capable of reflecting 95.5% of sunlight — only to outdo themselves a half of a year later, by creating one that’s even whiter.
Led by Xiulin Ruan, the university's professor of mechanical engineering, the research team formulated paint that reflects up to 98.1% of sunlight, which keeps paint covered surfaces cool and can potentially be a tool for curbing global warming. “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," explains Ruan. "That’s more powerful than the central air conditioners used by most houses.”
Currently, air conditioning accounts for 12% of U.S. energy consumption, and many air conditioners use hydrofluorocarbons (HFCs); while HFCs make up a small percentage of greenhouse gasses, they trap thousands of times the amount of heat as carbon dioxide.
“Radiative cooling is a passive cooling technology that offers great promises to reduce space cooling cost, combat the urban island effect, and alleviate global warming,” states the abstract in the team’s research paper. “To achieve passive daytime radiative cooling, current state-of-the-art solutions often utilize complicated multilayer structures or a reflective metal layer, limiting their applications in many fields.” But, the world’s whitest paint may be the solution.
One of the main ingredients responsible for the paint’s ultra whiteness is its very high concentration of a chemical compound called barium sulfate (BaSO4), which is also the whiting agent used to make photo paper and cosmetics. Particles of different sizes, rather than one size, allow the paint to scatter more of the light spectrum from the sun, giving it greater reflectance. Though the team could, possibly, still make the paint whiter, they can’t do it without compromising its quality.
Commercial white paint tends to get warmer rather than cooler. Even paint that is intended to reject heat tends to reflect roughly 80% to 90% of sunlight, and certainly can’t make surfaces cooler than their surroundings.
But, according to the Guinness World Records, with the new white paint “scientists estimate that it would only require 0.5–1% of Earth’s surface to be coated in this paint (e.g., by painting roofs) to reverse global warming to date.” Its whiteness also makes the paint the coolest on record. “Ruan and his colleagues tested BaSO4 using thermocouples, high-accuracy devices that measure voltage to determine temperature. They found that at night, BaSO4 surfaces are 19° F. cooler than surrounding air.”
The technique that the team used to create the paint is compatible with the commercial paint fabrication process. Roughly half the cost of the titanium dioxide powders that are often used in commercial white paints, Barium sulfate is common, cheap, and environmentally safe.
But, the whitest paint in the world is not yet ready for commercial use. The team still wants to optimize their paint for a wider range of applications; think automobiles and outdoor equipment. And to add a little color, which may not be as energy efficient, but definitely fun.
Note* Images are either in the public domain or available via Fair Use.