The engineers hope the supercool paint will reduce the need for air conditioning on a warming planet.
Last year, a Purdue University team unveiled a superwhite radiative cooling paint they said could basically create "free air conditioning" for houses and buildings. They've now developed an even whiter and cooler paint, one-upping their previous effort.
"The researchers believe that this white may be the closest equivalent of the blackest black, 'Vantablack,' which absorbs up to 99.9% of visible light," Purdue said in a statement Thursday. The white paint reflects up to 98.1% of sunlight, an improvement on the previous version's 95.5%.
Ultrablack coatings and paints like Vantablack and MIT's carbon-nanotube material (which doesn't have a catchy name) are finding uses in telescopes, on wristwatches and for art projects.
The research team has a very specific purpose in mind for its new whitest-white paint: helping people chill out. It could be used on buildings and houses to reduce the need for air conditioning and conserve energy. Purdue calls the paint "the coolest on record."
Surfaces painted with this whitest-white stay cooler than their surroundings, both under sunlight and at night, and it works in warm and cold conditions. "During an outdoor test with an ambient temperature of 43 degrees Fahrenheit, the paint still managed to lower the sample temperature by 18 degrees Fahrenheit," said Purdue.
The previous extremely white paint was made with calcium carbonate (a compound found in chalk), but the recipe for this new paint uses barium sulfate particles (found in some cosmetics).
"A high concentration of particles that are also different sizes gives the paint the broadest spectral scattering, which contributes to the highest reflectance," said Purdue doctoral student Joseph Peoples, co-author of a paper published Thursday in the ACS Applied Materials & Interfaces journal.
As paints and materials move to ever blacker blacks and whiter whites, is there room to improve on the new formula? According to co-author Xiangyu Li, not much. There are only so many particles that can be crammed into it without compromising the paint's durability.
With current commercial ultrawhite paints reflecting only up to 90% of sunlight, the Purdue paint's performance could make it the new answer to Outkast's enduring Hey Ya question. What's cooler than being cool? This paint.