Engineers at Purdue University have developed a paint so white that it actually cools surfaces. They hope that the new paint can help fight global warming by reducing reliance on air conditioning.
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“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,” Xiulin Ruan, a Purdue professor of mechanical engineering, said in a statement. “That’s more powerful than the central air conditioners used by most houses.”
The ultra-white paint reflects up to 98.1% of sunlight; compare that to similar paints on the market, which reflect 80-90% of sunlight. The new paint sends infrared heat away, which cools the painted surface. Paints currently on the market don’t have this power.
How is this paint so white? First, it contains a high concentration of barium sulfate, a chemical used to whiten photo paper and cosmetics. “We looked at various commercial products, basically anything that’s white,” said Xiangyu Li, a postdoctoral researcher who worked in Ruan’s lab. “We found that using barium sulfate, you can theoretically make things really, really reflective, which means that they’re really, really white.”
The other technological key to the bright white color is the size difference between barium sulfate particles in the paint. The size of a particle determines how much it scatters light, so the wide range of particle sizes means more scattering of the sun’s light spectrum.
Scientists have been trying to develop a radiative cooling paint as an A/C alternative since the 1970s. The new paint is the most successful attempt to date and can keep surfaces 19°F cooler at night than the ambient surroundings. Even in strong midday sunlight, the ultra-white Purdue paint can cool surfaces by 8°F.
While it’s possible to make the paint slightly whiter, the new paint is about as white as researchers can go without compromising quality. “Although a higher particle concentration is better for making something white, you can’t increase the concentration too much,” Li said. “The higher the concentration, the easier it is for the paint to break or peel off.”
Image via Jared Pike / Purdue University