‘World’s Whitest Paint' Gets New Formulation
WEDNESDAY, OCTOBER 5, 2022
Researchers at Purdue University have recently developed a new thinner, lighter formulation for its “whitest white” paint, making it ideal for cooling vehicles or aircraft.
Using nanoparticles of barium sulfate to reflect 98.1% of the sunlight, the white cooling paint can cool outdoor surfaces, but the research team knew certain structures would need a lighter formulation. The research has since been published in Cell Reports Physical Science.
The ‘Whitest White’ Cooling Paint
According to PaintSquare Daily News, the research team from Purdue University initially created an ultra-white paint in October 2020. Since then, the team has been pushing to reformulate it for even “cooler” properties.
In 2021, the team published a paper about its findings in the journal ACS Applied Materials & Interfaces.
At the time, researchers went as far as to say that their white paint was the closest thing available to an equivalent of “Vantablack,” which absorbs up to 99.9% of visible light. On the flip side, the new whitest paint reflects up to 98.1% of sunlight, compared to 95.5% in the researchers’ previously developed ultra-white paint. Typically, white coatings expect to reflect 80-90% of sunlight.
|
|
| Purdue University |
|
Researchers at Purdue University have recently developed a new thinner, lighter formulation for its “whitest white” paint, making it ideal for cooling vehicles or aircraft. |
“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, at the time.
There is one key element on achieving the white coating: barium sulfate.
“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.”
But it’s not just the high concentration of barium sulfate, it’s also that those particles are deliberately different sizes in the paint. How much light each particle scatters is directly dependent on its size, and a wider range of sizes allows the paint to scatter more of the light spectrum.
However, if there is too high of a concentration, the durability of the paint is negatively affected.
“Although a higher particle concentration is better for making something white, you can’t increase the concentration too much. The higher the concentration, the easier it is for the paint to break or peel off,” Li said.
To test the cooling traits of the paint, researchers used thermocouples to demonstrate outdoors that the paint can keep surfaces 19 degrees Fahrenheit cooler than the ambient surroundings at night, and 8 F below their surroundings during high noon. Reportedly, the paint even works in winter climates.
Patent applications for this paint formulation were filed through the Purdue Research Foundation Office of Technology Commercialization. The research was supported by the Cooling Technologies Research Center at Purdue University and the Air Force Office of Scientific Research through the Defense University Research Instrumentation Program. The research was performed at Purdue’s FLEX Lab and Ray W. Herrick Laboratories and the Birck Nanotechnology Center of Purdue’s Discovery Park.
Thinner Formulation
Now, the coating has been formulated to be thinner and lighter, making it ideal for radiating heat away from cars, trains and airplanes, according to a release from Purdue University.
“I’ve been contacted by everyone from spacecraft manufacturers to architects to companies that make clothes and shoes,” said Runa. “They mostly had two questions: Where can I buy it, and can you make it thinner?”
While the original white paint received recognition from Guinness World Records and “The Late Show With Stephen Colbert,” there was a problem with applying the coating to a roof or other structures.
“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.”
To resolve this, Ruan’s team began experiment with other materials to push the limit of its capability to scatter sunlight. According to Purdue’s release, the latest formulation is nanoporous paint incorporating hexagonal boron nitride as the pigment, a substance mostly used in lubricants.
As a result, the new paint achieves nearly the same level of solar reflectance at 97.9% with a single 150-micron layer of paint.
“Hexagonal boron nitride has a high refractive index, which leads to strong scattering of sunlight,” said Andrea Felicelli, a Purdue Ph.D. student in mechanical engineering who worked on the project. “The particles of this material also have a unique morphology, which we call nanoplatelets.”
Ioanna Katsamba, another Ph.D. student in mechanical engineering at Purdue, then ran computer simulations to understand if the nanoplatelet morphology offers any benefits.
“The models showed us that the nanoplatelets are more effective in bouncing back the solar radiation than spherical nanoparticles used in previous cooling paints,” Katsamba said.
Purdue reports that the paint also incorporates voids of air, which make it highly porous on a nanoscale. This, in combination with the thinner application, makes the new paint weigh 80% less than barium sulfate paint while achieving nearly identical solar reflectance.
“This light weight opens the doors to all kinds of applications,” said George Chiu, a Purdue professor of mechanical engineering and an expert in inkjet printing. “Now this paint has the potential to cool the exteriors of airplanes, cars or trains.
“An airplane sitting on the tarmac on a hot summer day won’t have to run its air conditioning as hard to cool the inside, saving large amounts of energy. Spacecraft also have to be as light as possible, and this paint can be a part of that.”
Ruan added that they are in discussions right now to commercialize the paint, while there are “still a few issues that need to be addressed, but progress is being made.”
“Using this paint will help cool surfaces and greatly reduce the need for air conditioning,” Ruan said. “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.”
White Paint for Cutting Emissions
Earlier this year, in May, reports considered how the coating from Purdue University could slash carbon emissions and, in some cases, replace air conditioning units. Detailing how white paint can keep buildings cool, the researchers’ study was published in Cell Reports Physical Science.
The reports have not only praised the coating for its potential to save energy, but also that the coating scatters the sunlight’s wavelengths so that it can exit through an atmospheric window.
A key feature in the coating development, the ability to send the sunlight's ray heat into deep space would create an infinite “heat sink,” according to 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. This is important not only in fighting the effects of global warming, but when air conditioners are used, they remove the heat and humidity from indoors and transfer it outdoors, increasing the overall heat sink effect of a city or town.
If applied on several surfaces, apart from buildings and other structures, researchers believe that we could witness a significant global cooling effect. According to the researchers at Purdue, their ultra-white paint could reduce air conditioning by up 70% in desert cities such as Reno, Nevada, and Phoenix, Arizona.
In a separate study published in Nature Geoscience, researchers found that by creating lighter surfaces by painting structures, roads and unused land, among other things, up to a 3 C decrease in temperatures could be witnessed during the summer months. The effort would improve public health and lower both electricity usage and carbon emissions.
Tagged categories: Coating chemistry; Coating Materials; Coatings; Coatings technology; Coatings Technology; Colleges and Universities; Cool Coatings; Formulating; Paint; Reflective coatings; Research and development
