What we perceive as a white shade or color in our everyday lives is never pure white. True white is a rarity that can only be observed in unfiltered sunlight, just as pure black can only be found in the depths of a black hole. For even the whitest human-made pigments, a close examination will reveal something a little bit off … off-white, that is.
But now, there’s exciting news coming from Indiana’s Purdue University, where scientists announced yesterday September 16, that they were able to produce the whitest acrylic paint known to humankind. If you’re not convinced, the university has already earned a Guinness World Records title for the invention.
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However, breaking a record for the whitest paint was not the researchers’ initial motivation. Rather, it was combating global warming.
“When we started this project about seven years ago, we had saving energy and fighting climate change in mind,” said Xiulin Ruan, a professor of mechanical engineering at Purdue, in a podcast episode of This Is Purdue.
Ruan invented the paint with his graduate students at Purdue. Their original goal was to create a paint that would effectively reflect sunlight away from a building, which required producing an extremely white pigment. Ruan says that the formulation that his lab created reflects 98.1% of solar radiation while also emitting infrared heat. Because the paint absorbs less heat from the sun than it emits, a surface coated with this pigment is cooled below the surrounding temperature without consuming power.
What makes this invention unique is that typical commercial white paint tends to get warmer, rather than cooler, when exposed to sunlight. Paints on the market that are designed to reject heat reflect up to 80%-90% of sunlight and usually fail to make surfaces cooler than their surroundings.
Using this new paint formulation to coat a roof area of about 1,000 square feet could result in a cooling power of 10 kilowatts, the researchers showed in a peer-reviewed paper. “That’s more powerful than the air conditioners used by most houses,” Ruan asserted.
The researchers found that the ultra-white paint is able to keep a surface around 8 degrees cooler than its ambient temperature in the afternoon and up 19 degrees cooler at night. When tested on buildings in the hot, dry climates of Reno, Nevada, and Phoenix, Arizona, the paint reduced air conditioning costs by 70% during the summer months, according to Ruan.
Research to develop radiative cooling paint as a sustainable alternative to traditional air conditioners goes back to the 1960s. To create their achievement, Purdue’s researchers used a very high concentration of the chemical compound barium sulfate — also used in photo paper and cosmetics — in different particle sizes. The wide range of particle sizes is a key factor because it allows the paint to reflect more wavelengths of the sun, therefore scattering more of the light spectrum.
But there was a limit to how much barium sulfate the researchers could use before the paint starts breaking or peeling off. “There is a little bit of room to make the paint whiter, but not much without compromising the paint,” they said. The team is also working on producing cooling color paints using the same technology.
Artists and art museums have already expressed interest in the new paint, according to Ruan. “Artists have emailed me asking where they can get the paint,” he said in the podcast interview, adding that his team sent samples of the rare pigment to museum collections worldwide.
“I didn’t expect people to be so interested in white,” the researcher said. “White to me, before all this, was a boring color … It’s good to know that there’s a market on the art side, aside from the energy and climate aspects.”
So, when will you be able to buy the paint at your local hardware store? According to Ruan, the paint will hit the shelves in a “year or two.” His team has filed patent applications for the paint and partnered with a commercial company to scale up production and put it on the market. The cost will be comparable to existing paints, or even slightly cheaper. If all goes as planned, a day will soon come when costly, energy-consuming air conditioners are no longer a necessity.