Scientists from the University of Maryland (USA) have created a fabric that regulates its thermal properties in response to changes in humidity and temperature of the human body. The material, described today in ScienceIt has the appearance of a kitchen cloth, but is woven with threads that modify the braid of its fibers to dissipate or retain infrared radiation, which is one of the main forms of heat exchange of the human body. The process is automatic and does not require any input of energy. In addition, the textile material they have used can be manufactured, washed and dyed like any fabric.
The threads are formed by cellulose fibers covered by a metamaterial, Carbon nanotubes. In the heat or humidity, each thread is compressed. This has two complementary effects. On the one hand, it increases the size of the pores in the general mesh of the fabric. It becomes more breathable and this favors the cooling of the body, by evaporation of the sweat and convection of the air on the skin. But, in addition, the compression of the threads brings each one of the fibers that compose them.
By placing in proximity the carbon nanotubes that cover these fibers, an electromagnetic coupling occurs between them and all the tissue starts to emit infrared radiation, dissipating the heat transmitted by the body. On the contrary, in a cold or dry environment, the fibers covered with nanotubes that form each thread are spaced, which reduces their interaction and thermal radiation. This expansion of the yarns also causes the pores of the fabric to become smaller. All this helps to retain body heat.
"We are interested in marketing this product," says Ouyang Min, one of the researchers who has developed the material. Min has explained to Matter that the product is already patented and, in the absence of "optimizing the design and performance", it can be used in the manufacture of clothing. It would be especially useful, for example, in sportswear, since the reaction of the threads to heat and moisture would be activated in response to sweat. "We have also thought about other applications," he adds. One of them is painting for the exterior of buildings in order to improve their energy efficiency.
Although the manufacturing process is somewhat more expensive than conventional fabrics, Min says that it will have a very reasonable cost, and that it is compatible with existing commercial processes. Carbon nanotubes are added to the cellulose fibers by a process similar to solution dyeing, and in addition there is no need to add much material because the best performance is achieved with very low concentrations of carbon.
Agustin Mihi, a scientist from the Institute of Materials Science of Barcelona (ICMAB-CSIC), says the study is "groundbreaking" for developing in detail a theoretical concept of photonics and bring it to a practical and tangible use. "It's ironic that now, when we stop using paper and everything is electronic, cellulose advances, evolves and finds other applications," says Mihi. He and his colleagues from ICMAB have also made progress with this "fashionable" material, for example by creating a type of paper that generates electricity of heat and also by adding nanostructures to cellulose for give it different colors without using any colorant.
In the field of thermal control, other researchers have created materials that achieve the effect of radiant cooling, for example with fabrics that reflect sunlight or that allow body radiation to escape. However, the creators of the new fabric assure that none of these previously presented materials was able to respond to their environment to regulate both the cooling and warming of the body.