Ultra-white is the new Vantablack. Researchers at Purdue University have developed the whitest white paint ever. Reflects 98.1% of sunlight. (The blackest paint, Vantablack, absorbs 99.9% of visible light.) According to lead researcher Xiulin Ruan, “if you used this paint to cover a roof area of about 1,000 square meters, we estimate that you could have a cooling power of 10 kilowatts. It is more powerful than the central air conditioners used by most homes. “From Purdue:
Two characteristics give the paint its extreme white. One of these is the very high concentration of paint in a chemical compound called barium sulfate, which is also used to make white paper and cosmetics.
“We looked at various commercial products, practically anything is white,” said Xiangyu Li, a postdoctoral researcher at the Massachusetts Institute of Technology who worked on the project as a Purdue Ph.D. student in Ruan’s lab. “I found that using barium sulfate, theoretically you can make things really, really reflective, which means they’re really, really white.”
The second feature is that barium sulfate particles have different sizes in the paint. How much particle scatters light depends on its size, so a wider range of particle sizes allows the paint to scatter more of the spectrum of sunlight.
“A high concentration of particles, which also have different sizes, gives the paint the widest spectral spread, which contributes to the greatest reflectance,” said Joseph Peoples, a Purdue PhD. mechanical engineering student.
There is a little room to make the paint whiter, but not much without compromising the paint.
“Although a higher concentration of particles 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 sun’s reflective paint is so effective that it worked even 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.
photo above: Jared Pike / Purdue University