Effective for heat measures? The whitest paint on the planet

According to a paper recently published in the journal ACS Applied Materials & Interfaces, Purdue University researchers announced that they developed the whitest white paint on the planet that reflects up to 98.1% of light. The research team announced that it had developed a 95.5% reflective paint for sunlight last fall, but this time it was announced that it exceeded that.

Of course, you may think that the difference from the white paint sold in the actual store is not so great, but even a few percent is important for the cooling effect of white paint. Everyone knows that in summer when the sun is strong, it’s better to wear white than black. White reflects light and black absorbs light.

The research team revealed that the super-reflective, highly-reflective white paint currently on sale reflects only 80-90% of light. I think that 90% and 98% are not that different, but you have to think about the absorption rate of sunlight. The developed paint absorbs 1.9% of the sun, but if you use a commercial paint reflector, it absorbs 10%. Five times higher than the amount this paint absorbs. Just because it looks white, it explains that the existing white paint cannot cool beyond the ambient temperature.

In addition, according to the research team, the development of the whitest paint with cooling effect was taking place in the 1970s. The research team has been working on whitening white paint more than seven years ago, and has been looking for a way to add a material that reflects sunlight to the paint. This time, we developed a white paint containing barium sulfate, which is used in white cosmetics and photographic paper, in a high concentration and containing particles of different sizes. The reason why the color of the sun is different is that the wavelengths are different, because different size particles are required to hit each wavelength.

The development of such super reflective paints could significantly change the way buildings are designed as the earth is warming. For example, if you change the asphalt roof surface, which is highly absorbent at high temperatures, to a reflective material, or prepare green areas such as buildings or city parks that have been greened on the roof, and cool the area, you can beat the heat without using the energy to run the air conditioner. Help.

The research team estimates that using super-reflective whitewash on a large scale in cities such as Reno, Nevada, and Phoenix, Arizona, can reduce air conditioning costs by up to 80%. Of course, not all problems can be solved by doing such a climate hack. When considering urban design including heat measures, there are many things to consider realistically. In order to increase urban reflectivity, roofs and walls using reflective materials must operate normally. Even if the reflectivity is high at 95% at first, pollutants, water droplets, and soot in the air may adhere to the surface, resulting in a decrease in reflectivity.

If all roofs that need to be replaced can be converted to highly reflective ones, all roofs can be highly reflective roofs in 10 to 30 years, and the use of reflective materials can be promoted according to the timing of the roof replacement without the need for specific skills such as coatings. Related information can be found here.