A new formula for white paint gives us the whitest white yet. It reflects 98.1 percent of all the light it hits, which is significantly cooler than ambient temperature, even when sitting in full sunlight.
The inventors say that the paint is used to cover buildings, but it can help in the fight against global warming by reducing our dependence on air conditioning with electricity, a habit that exacerbates the climate crisis.
‘If you were to use this paint to cover a roof area of about 1000 square feet [92.9 square meters]”We estimate that you can get a cooling of 10 kilowatts,” said mechanical engineer Xiulin Ruan of Purdue University.
“It is more powerful than the central air conditioners that most homes use.”
The work of the team builds on paint they developed last year, which reached a then record level of 95.5 percent. The new formula, according to the team, brings it much closer to being a true counterpart to Vantablack, the black pigment that absorbs up to 99.965 percent visible light.
The image below, in optical light on the left and infrared on the right, shows how cooler the painted surface is than the surrounding surface.
(Purdue University / Joseph Peoples)
Vantablack has its own applications, but engineers and materials scientists have been chasing an ultra-reflective white paint for a while for its potential cooling. Reflective cooling paints are already commercially available, such as titanium dioxide paints, but they can not achieve cooler than their environment.
To develop their new paint, the researchers looked for white reflective materials. Their previous paint was made of calcium carbonate particles – the chemical compound found in chalk, limestone and marble – suspended in an acrylic paint medium.
For their new formula, they turned to barium sulfate, which occurs naturally as a mineral barite, and is usually used as a pigment in white paint.
“We looked at different commercial products, basically everything that is white,” said mechanical engineer Xiangyu Li of the Massachusetts Institute of Technology, formerly at Purdue.
“We found that you could make barium sulphate things really reflective in theory, which means it’s really white. ‘
The trick is the size and concentration of the particles. A range of different barium sulphate particle sizes allows the paint to disperse the maximum amount of light, and of course, the more barium sulphate there is, the more light it can reflect. However, there is a point at which too much barium sulphate can impair the integrity of the paint and make it brittle and flaky when dried.
The sweet spot, the researchers found, is a concentration of about 60 percent barium sulfate in the acrylic medium.
Xiulin Ruan stops a sample of the paint. (Purdue University / Jared Pike)
During field tests, the team found that their painted surface could remain cooler than the ambient temperature at least 4.5 degrees Celsius throughout, achieving an average cooling capacity of 117 watts per square meter. It sustained it even in the death of winter.
By comparison, the team’s calcium carbonate paint had an area temperature of more than 1.7 degrees Celsius in the afternoon and a cooling power of 37 watts per square meter – so the single extra percentage of reflection in the barium sulphate paint made a significant difference. made.
Due to the limitations of the materials, the barium sulphate paint probably can not get much more reflective, but what the team has achieved can actually change the world for the better.
Air conditioning injects heat into the earth’s atmosphere in various ways, including expelling hot air from buildings, the heat from running the machines, and the electricity normally generated by fossil fuels, which contribute to the release of carbon dioxide.
Scientists have been looking for a method of passive cooling since the 1970s. This barium sulfate paint works, it is reliable and can be easily manufactured. The team has filed a patent and hopes the paint can be used in general soon.
And then? Maybe we should license it for use to all artists except one.
The research was published in ACS applied materials and interfaces.