The New "Mirror" Fabric Can Cool Consumers Down To Almost 5°C Researchers To Question Its Durability.
While it's easy to design clothes that keep you warm, it's much more difficult to wear clothes that keep you cool on a hot summer's day. Researchers have now created a fabric that looks like an everyday T-shirt but can cool the body to nearly 5°C. They say the technology, if mass-produced, could help people around the world protect themselves from rising temperatures caused by climate change.
To make clothes that reflect sunlight, fashion designers usually use light fabrics that reflect visible light. But other methods reflect the sun's electromagnetic radiation, including ultraviolet (UV) and near-infrared (NIR) radiation. NIR heats the object that absorbs it and slowly cools it as it emits. However, this cooling process is hindered by our atmosphere: Upon emission from an object, NIR is often absorbed by nearby water molecules and warms the surrounding air.
The researchers turned to mid-infrared radiation to accelerate the cooling process, a type of IR with longer wavelengths. Instead of being absorbed by molecules in the ambient air, MIR energy goes directly into space and cools objects and their surroundings. This technique is known as radiant cooling and used by engineers for the past decade to design roofs, plastic sheeting, wood, and ultra-white paint.
Human skin, we were unlike many of the clothes, radiates ME naturally. So in 2017, researchers at Stanford University developed a network that allows MIR to penetrate directly from the human body and cool the user by around 3°C. But for this to work, the fabric must be extremely thin - only 45 microns, or about one-third the thickness of a light linen shirt. As a result, it has led some researchers to question its durability.
To create a denser fabric, engineers Ma Yaoguang of Zhejiang University and Tao Guangming of Huazhong University took a different approach. Instead of allowing the skin's MIR directly through its tissues, he and his colleagues designed a textile that absorbs body heat through chemical bonds and radiates its energy into space as MIR.
As a result, the 550-micrometer fabric - made from a mixture of lactic acid and synthetic fibers with dispersed titanium dioxide nanoparticles - also reflects UV, visible, and NIR rays and cools the wearer. Although it looks like an ordinary shirt, "optically it is a mirror," Tao said.
The researchers put together a fitted cardigan, half made of their fabric and the other half of white cotton about the same obesity to test their creation. Then, graduate students put on vests and sit on grass chairs in direct sunlight for 1 hour. When researchers measured the skin temperature, the side under the new fabric was nearly 5°C cooler than the side under the cotton, Science reported today. The contrast is evident with the infrared camera, and Tao says students can feel the temperature difference.
"Everything is interesting," said Yi Cui, a Stanford materials scientist who led the previous research and whose lab in the center of IR continues to work on transparent fabrics. But because MIR-emitting technology has so far was used on solid surfaces that are constantly facing the sky, the authors of this new work also needed to measure how well their fabrics cooled when standing or walking. He also wondered if the material was loose because the cooling element relies on close touch with the skin.
A mechanical engineer at the Massachusetts Institute of Technology shared some of Cui's concerns. However, he added that the work spoke of rapid advances in the field of radiation cooling. "There are advantages to this approach as it allows a wider use of the material and feels more like cotton, which is important to consumers."