Apr 16, 2021 17:00:00

The 'whitest paint' has been developed that reflects more than 98% of light, and it's so white that it cools down objects it's painted on.

by Purdue University/Jared Pike

Engineers at Purdue University in the United States have developed the 'whitest paint ever made,' which reflects 98.1% of light. This paint, which is a counterpart to

Vantablack , the 'blackest substance on earth' that absorbs up to 99.9% of light, reflects not only visible light but also infrared rays that transmit heat, preventing objects from being heated by sunlight and making it useful for air conditioning and global warming countermeasures.

The whitest paint is here – and it's the coolest. Literally. - Purdue University News
https://www.purdue.edu/newsroom/releases/2021/Q2/the-whitest-paint-is-here-and-its-the-coolest.-literally..html

World's Whitest Paint: How Can It Fight Global Warming? | Science Times
https://www.sciencetimes.com/articles/30695/20210415/world-s-whitest-paint-science-invention-help-fight-global-warming.htm

White roofs reflect sunlight, preventing it from heating the earth's surface and reducing the need for air conditioning. This is why Nobel Prize-winning physicist Steven Chu has suggested that ' to stop global warming, all roofs in the world should be painted white .'

Therefore, a research team led by Shiulin Luan, a professor of mechanical engineering at Purdue University, studied more than 100 types of materials, selected 10 from them, and tested each material in 50 different ways to develop a 'white paint that reflects 95.5% of light'. From the article below, you can see a movie of an experiment to confirm the cooling effect using the paint.

'Ultimate white paint' that reflects 95.5% of light is developed - GIGAZINE

After further trial and error to improve the paint, the research team focused on barium sulfate , which is widely used in cosmetics, medicines, pigments, etc. They discovered that by using barium sulfate, sometimes called 'blanc fixe' in French, as a paint, they could achieve a reflectivity that exceeded that of the previous paint made from calcium carbonate.

Below are pictures of a board coated with the newly developed paint exposed to sunlight taken with a normal camera (left) and an infrared camera (right). As you can see from the photo on the right, the areas coated with white paint and the board with the paint are darker, which shows that the paint has a cooling effect not only on the paint itself but also on the object it is painted on.

by Purdue University/Joseph Peoples

The reason the paint is so white is because the barium sulfate particles are non-uniform: the amount of light scattering they do depends on the size of the particles, so the greater the difference in particle size, the more they can scatter a larger portion of the sunlight's spectrum .

When the research team measured the reflectivity of the paint, they found that the newly developed paint was able to reflect 98.1% of the sunlight. This means that only 1.9% of the heat was absorbed, and the cooling effect was twice as much as the previous paint. Thanks to this cooling effect, the object coated with the paint was 4.4 degrees cooler than the surroundings in the sunlight and 10.5 degrees cooler at night.

'We estimate that applying this paint to a 1,000-square-foot (about 93 square meters) roof would provide a cooling effect equivalent to 10 kilowatts, which is more powerful than most household air conditioners,' said Luan. The technology that Luan and his team used to develop this paint is compatible with the process for manufacturing commercially available paints, making it easy to put into practical use.