When you think of revolutionary technology, white paint is probably not even remotely close to being on your list. But, believe it or not, there’s been a recent breakthrough in some paint technology that will enable paint to cool buildings. Sound too good to be true? Read on:
Your average commercial white paints reflect 80-90% of sunlight, failing to keep buildings cool during the day. However, all of the is changing because of the research of mechanical engineer, Xiulin Ruan at Purdue University in West Lafayette, Indiana, and his colleagues. They sought to create whiter paints to cool buildings “similar to an air conditioner, but without the need of electricity,” he said. They explored more than 100 materials, narrowing them down to 10 and testing roughly 50 different formulations of each material.
Barium sulfate, a compound used to whiten photo paper and cosmetics, performed the best. Its molecular structure can make it highly reflective to solar wavelengths of light. When it does absorb energy from heat or other sources, it typically emanates it out at infrared wavelengths that zip unobstructed through air into outer space instead of heating its surroundings.
The new paint reflects up to 98.1% of sunlight, compared with the 95.5% of sunlight reflected by the researchers’ previous ultra-white paint based on calcium carbonate. They suggest this white may be the equivalent of the blackest black, “Vantablack,” made using carbon nanotubes, which absorbs up to 99.9% of visible light.
Outdoor tests of the new paint revealed it was the coolest on record, keeping surfaces 19 degrees Fahrenheit cooler than their surrounding surfaces at night, and 8 degrees cooler than surroundings under strong noon sunlight. It even worked in the middle of winter — when the ambient temperature was 43 degrees Fahrenheit, it still managed to lower temperatures by 18 degrees Fahrenheit. (This latter quality suggests this paint might work best for hot climates that would benefit most from cooling, although Ruan notes they “may come up with dynamic paints that can switch properties for other climates in the future.”)
Barium sulfate is common and environmentally safe, and powders of it are roughly half the cost of the titanium dioxide powders often used in commercial white paints, Ruan said. The scientists also noted the methods they used to make their paint are compatible with commercial paint fabrication techniques, and can likely handle conventional outdoor conditions.
In the future, the researchers want to optimize and commercialize their paint for a wide range of applications, including buildings, automobiles and outdoor equipment. They would also like to develop colored versions, which won’t achieve as much cooling but “can still provide significant energy savings compared to commercial paints of the same color,” Ruan said.
Read more in their report here: https://pubs.acs.org/doi/10.1021/acsami.1c02368
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