WEST LAFAYETTE, Ind. (AP) – A new paint developed by researchers at Purdue University is the coolest – literally. When Xiulin Ruan, a professor of mechanical engineering at the school, and his graduate students began working on this project seven years ago, they didn’t set out to invent a new paint color. Rather, they wanted to find a way to conserve energy and fight climate change. But what they found is that paint could do just that. And so Ruan and his team created the world’s whitest paint – a title it recently earned in the Guinness World Records book, a never achieved status. This paint, however, can do much more than set world records. It is considered a breakthrough in sustainability, one that could reduce or even eliminate the need for air conditioning, and thus the energy needed to power it. ‘œThe impact of this paint, it’s good for trying to alleviate global warming, the urban heat island effect and the electricity crisis,’� said Xiangyu Li, a postdoctoral researcher at the Massachusetts Institute of Technology who worked on this project as a Ph.D. student in Ruan’s lab. ‘œBut the part I like the best is that it could directly impact peoples’ electricity bills, and that’s something everyone can relate to.’� Developing the formula for this paint wasn’t easy. The multiple-year study builds on efforts to create a cooling paint as an alternative to traditional air conditioning that dates back to the 1970s. The researchers considered over 100 different materials and narrowed their options down to 10. From there, the lab tested about 50 different formulations for each material. ‘œI started looking at every white material in my daily life,’� Li said. That’s when they found barium sulfate. The paint is based on two key features: the concentration and size of the barium sulfate compound. The paint has a very high concentration of the compound, which is also used to make photo paper and cosmetics white. It also has particles of the barium sulfate that are of all different sizes in the paint. Most white paints have one single particle size that reflects the visible portion of the solar spectrum, but they absorb more ultraviolet and infrared light, according to Joseph Peoples, a Ph.D. candidate in Purdue’s School of Mechanical Engineering who also worked in Ruan’s lab. ‘œThe ‘‹largest difficulty was making the paint as reflective as possible for the entire solar spectrum,’� Peoples said. The amount of light each barium sulfate particle scatters depends on its size, Peoples said. So having a wider range of particle sizes allows the paint to scatter more of the full light spectrum. The researchers think that this whitest white paint is likely the closest equivalent to Vantablack, the blackest black paint that absorbs up to 99.9% of visible light. The paint that Ruan’s lab landed on reflects up to 98.1% of sunlight, according to the research. This compares to the other highly reflective paints on the market that reflect between 80 to 90% of light. Because Ruan’s paint reflects almost all incoming sunlight, it’s not taking on any energy. Then it goes a step further, emitting thermal energy into outer-space beyond Earth’s atmosphere, meaning it sends out more heat than it takes in. ‘œLet’s say it is a dry sunny day outside and the temperature is 85 degrees Fahrenheit,’� a surface covered with the paint from Purdue ‘œwill be around 75 degrees Fahrenheit,’� Peoples said. ‘œThe paint cools itself below ambient, creating free refrigeration, with no electricity input at all.’� By lowering the surface temperatures of buildings painted with this white paint, it also lowers the inside temperatures of said buildings. If buildings aren’t heating up from sunlight, then that lowers the need to switch on their air conditioning as high or removes it entirely.

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