The world’s whitest paint.
The world’s whitest paint – seen in this year’s edition of Guinness World Records and “The Late Show With Stephen Colbert” – is so effective at keeping surfaces cool that it could reduce the need for air conditioning. Now the Purdue University researchers who created the paint have developed a new formulation that is thinner and lighter – ideal for radiating heat away from cars, trains and airplanes.
Whiter, brighter & more reflective
Their original formula for the whitest paint employed barium sulphate nanoparticles to reflect 98.1% of sunlight, lowering the temperature of outdoor surfaces by more than 4.5°C. Imagine painting your roof in that paint, which would greatly decrease the need for air conditioning. However, there is an issue.
It’s common knowledge that white surfaces reflect more heat than dark colours so how is this white paint different? Typical commercial white paint gets warmer rather than cooler. Paints on the market that are designed to reject heat reflect only 80%-90% of sunlight and can’t make surfaces cooler than their surroundings. With its more reflective formulation the paint doesn’t absorb as much heat and the way it reflects means that objects surrounding it also don’t get as hot.
“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 characteristic is that the barium sulphate particles in the paint are all different sizes. A larger variety of particle sizes permits the paint to scatter more of the sun’s light spectrum since the amount of light that each particle scatters depends on its size.
“To achieve this level of radiative cooling below the ambient temperature, we had to apply a layer of paint at least 400 microns thick,” Ruan said. “That’s fine if you’re painting a robust stationary structure, like the roof of a building. But in applications that have precise size and weight requirements, the paint needs to be thinner and lighter.”
“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. That’s more powerful than the central air conditioners used by most houses,” said Xiulin Ruan, a Purdue professor of mechanical engineering.
This new development has opened up the possibilities for where the paint could be used, for example cars, planes and even spacecrafts. “This not only saves money, but it reduces energy usage, which in turn reduces greenhouse gas emissions. And unlike other cooling methods, this paint radiates all the heat into deep space, which also directly cools down our planet. It’s pretty amazing that a paint can do all that.”