Ultra-white is the new Vantablack. Purdue University researchers developed the whitest white paint ever. It reflects 98.1% of sunlight. (The blackest black paint, Vantablack, absorbs 99.9% of visible light.) According to lead researcher Xiulin Ruan, "f 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. That's more powerful than the central air conditioners used by most houses." From Purdue:
Two features give the paint its extreme whiteness. One is the paint's very high concentration of a chemical compound called barium sulfate, which is also used to make photo paper and cosmetics white.
"We looked at various commercial products, basically anything that's white," said Xiangyu Li, a postdoctoral researcher at the Massachusetts Institute of Technology, who worked on this project as a Purdue Ph.D. student 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 second feature is that the barium sulfate particles are all different sizes in the paint. How much each particle scatters light depends on its size, so a wider range of particle sizes allows the paint to scatter more of the light spectrum from the sun.
"A high concentration of particles that are also different sizes gives the paint the broadest spectral scattering, which contributes to the highest reflectance," said Joseph Peoples, a Purdue Ph.D. student in mechanical engineering.
There is a little bit of room to make the paint whiter, but not much without compromising the paint.
"Although a higher particle concentration is better for making something white, you can't increase the concentration too much. The higher the concentration, the easier it is for the paint to break or peel off," Li said[…]
The paint's solar reflectance is so effective, it even worked in the middle of winter. 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.
top photo: Jared Pike/Purdue University
