Scientists at the University of Maryland claim to have discovered a new material that can heat or cool automatically depending on the surrounding conditions.
The fabric is said to change its insulating properties in response to the environment. For example, when conditions are warm and moist, such as those of a sweating body on a summer day, the fabric allows infrared radiation (radiant heat) to pass through. When conditions become cooler and drier, the fabric reduces the heat that escapes. Infrared radiation is a primary way the body releases heat and is the focus of this new technology.
The base yarn for this new textile is created with fibres made of two different synthetic materials — one absorbs water and the other repels it. The strands are coated with carbon nanotubes, a special class of lightweight, carbon-based, conductive metal. Because materials in the fibres both resist and absorb water, the fibres warp when exposed to humid conditions such as surrounding a sweating body. That distortion brings the strands of yarn closer together, which does two things. First, it opens the pores in the fabric which has a small cooling effect because it allows heat to escape. Second, it modifies the electromagnetic coupling between the carbon nanotubes in the coating.
“This is the first technology that allows us to dynamically gate [regulate] infrared radiation,” says YuHuang Wang, a UMD professor of chemistry and biochemistry and one of the paper’s corresponding authors.
“You can think of this coupling effect like the bending of a radio antenna to change the wavelength or frequency it resonates with,” Wang adds. “It’s a very simplified way to think of it, but imagine bringing two antennae close together to regulate the kind of electromagnetic wave they pick up. When the fibres are brought closer together, the radiation they interact with changes. In clothing, that means the fabric interacts with the heat radiating from the human body.”
Depending on the tuning, the fabric either blocks infrared radiation or allows it to pass through. The reaction is almost instant, so before people realise they’re getting hot, the garment could already be cooling them down. On the flip side, as a body cools down, the dynamic gating mechanism works in reverse to trap in heat.
More work is needed before the fabric can be commercialised, but according to the researchers, materials used for the base fibre are readily available and the carbon coating can be easily added during the standard dyeing process.
Ray Baughman, a professor of chemistry at the University of Texas, comments: “This pioneering work provides an exciting new switchable characteristic for comfort-adjusting clothing,”
“Textiles were known that increase porosity in response to sweat or increasing temperature, as well as textiles that transmit the infrared radiation associated with body temperatures. However, no one before had found a way to switch both the porosity and infrared transparency of a textile so as to provide increased comfort in response to environmental conditions.”