A new formula for white paint has given us the whitest white so far. It reflects 98.1% of all the light that hits it and stays significantly colder than room temperature, even when sitting in full sunlight.
If used to line buildings, its inventors say, paint could help fight global warming by reducing our dependence on air-powered power, a habit that worsens the climate crisis.
“If you use this paint to cover a ceiling area of about 1,000 square feet [92.9 square meters], we estimate you could get a cooling capacity of 10 kilowatts, ”said mechanical engineer Xiulin Ruan of Purdue University.
“It’s more powerful than the central air conditioners most homes use.”
The team’s work is based on the painting they developed last year, which achieved a record reflection rate of 95.5%. The new formula, the team said, brings it much closer to being a true counterpart to Vantablack, the black pigment that absorbs up to 99.965 percent of visible light.
The following image, with optical light on the left and infrared on the right, shows how much colder the painted surface is than the surrounding surface.
(Purdue University / Joseph Peoples)
Vantablack has its own applications, but engineers and materials scientists have been pursuing an ultra-reflective white paint for a while, for its possible cooling capabilities. Reflective cooling paints are already commercially available, such as titanium dioxide paint, but do not reach lower temperatures than those in their environment.
To develop their new painting, the researchers looked for highly reflective white materials. His earlier painting was made of calcium carbonate particles (the chemical compound found in gypsum, limestone, and marble) suspended in an acrylic paint medium.
For their new formula, they were devoted to barium sulphate, which appears naturally as a mineral barite, and is commonly used as a pigment in white paint.
“We looked at several commercial products, basically anything that is white,” mechanical engineer Xiangyu Li of the Massachusetts Institute of Technology said earlier in Purdue.
“We’ve found that with barium sulfate, things can theoretically be made to be really reflective, which means they’re really very white.”
The trick is the size and concentration of the particles. A range of different sizes of barium sulphate particles 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. There is, however, a point where too much barium sulfate can compromise the integrity of the paint, making it brittle and flaky when dry.
The researchers found that the sweet spot is a concentration of about 60% barium sulfate in the acrylic medium.
Xiulin Ruan holds a sample of the painting. (Purdue University / Jared Pike)
During the field tests, the team checked that its painted surface managed to stay constantly colder than room temperature at least 4.5 degrees Celsius, achieving an average cooling power of 117 watts per square meter. He even kept it in the middle of winter.
In comparison, the equipment’s calcium carbonate paint had a surface temperature above 1.7 degrees Celsius below ambient at noon and a cooling power of 37 watts per square meter;
Due to the limitations of the materials, barium sulfate paint probably can’t get much out of it month thoughtful, but what the team has achieved could change the world for the better.
Air conditioning injects heat into the Earth’s atmosphere in a number of ways, including the release of hot air from buildings, the operating heat of machines, and the electricity usually generated by fossil fuel that makes them work that contributes to carbon dioxide emissions
Scientists have been looking for a method of passive radiative cooling since the 1970s. This barium sulfate paint works, is reliable and can be produced commercially very easily. The team has filed a patent and hopes the paint can soon be put to common use.
And then? Maybe we should license it for use by all but one of the artists.
The research has been published in Materials and interfaces applied by ACS.