Keqiao Li1,Yang Li1,Baoling Huang1
The Hong Kong University of Science and Technology1
Keqiao Li1,Yang Li1,Baoling Huang1
The Hong Kong University of Science and Technology1
The dynamic control of infrared (IR) radiation from surfaces is highly desired in a variety of areas. In particular, smart textiles, which can passively cool/warm the human body by regulating the radiative heat exchange with the environment, have aroused significant interest. Unlike air conditioners, such smart textiles can locally regulate the skin temperature without heating/cooling the entire building interior space, which is more efficient and energy-saving. In addition to the modulation of IR emissivity (ε) in a continuous manner over a wide range, adaptive textiles need to satisfy other requirements in flexibility, wearability, and water/air permeability, making it challenging to realize. Here, we report an infrared chromism phenomenon found in stacked Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> MXene nanosheets, where the emissivity varies in a wide range of 0.12 to 0.68 as the adsorption/desorption of physisorbed water within the interlayers of stacked nanosheets. This emissivity modulation is a continuous and reversible process without the assistance of any external device and energy input. By intercalating cellulose nanofibers into the Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> interlayers, the stability of water adsorption is significantly enhanced, making the dynamic process highly repeatable. Based on this water-induced emissivity modulation, we demonstrate a sweat-responsive adaptive textile that can help the human body adapt to fluctuations in personal heat load. When the human body feels cold and keeps dry, the textile is in low-<i>ε</i> modes where thermal radiation of the human body outwards can be suppressed to keep warm; otherwise, the textile can switch to wet states and high-<i>ε</i> modes. The radiative heat dissipation is enhanced significantly for cooling the human body. Besides the application in personal thermal management, this strategy may also find opportunities in other scenarios requiring adaptive IR emissivity regulation, including IR camouflage and IR anti-counterfeiting.