Controlling thermal radiation is crucial in various industries and applications. In particular, infrared emissions from the body are important since body temperature can be regulated without the use of external energy sources i.e. heater and air conditioner. Previous studies have shown that when materials which reflect radiation from the body are worn, the wearer’s body temperature increases. However, the majority of these materials are metal with a distinc­tive color, making it challenging to use textiles in other colors. Addi­tionally, they reflect most solar light, which makes the absorption of sunlight for outside warming difficult. 

To address these problems, Lili Cai and her team at University of Illinois Urbana-Champaign recently devised a visibly transparent infrared reflective coating. Designed with a nano-mesh structure, their new coating suffi­ciently transmitted visible light – including sunlight – and reflected body thermal radiation like conven­tional metal-based textiles. They were also able to utilize various colors of textile to achieve a warming effect without energy consump­tion. 

In addition, by combining their nano-pore structure with a photo­thermal material, the researchers were able to confine both sunlight and thermal energy from the body inside the textile. Even in freezing weather, their coating achieved a 15°C higher heating effect than commer­cial clothing – which could allow more outdoor acti­vity during the winter months without the need for bulky clothing. 

Applications for this technology go beyond personal heat management, however. The reflective properties of the team’s newly developed coating can be used in counter-sur­veillance military appli­cations – specifi­cally, to provide camouflage under the scrutiny of thermal imaging cameras. Their tests of the thermal camou­flage effect, at temperatures ranging from 34° to 250°C were so promising that it could success­fully be used for both daytime and nighttime cloaking. (Source: U. Illinois)

Reference: H. K. Woo et al.: Visibly Transparent and Infrared Reflective Coatings for Personal Thermal Management and Thermal Camouflage, Adv. Func. Mat. 32, 2201432 (2022); DOI: 10.1002/adfm.202201432

Link: Thermo-Nano-Manufacture for Energy & Wearables, Dept. of Mechanical Science and Engineering, University of Illinois at Urbana−Champaign, Urbana, USA