Self-regulating heating and self-powered flexible fiber fabrics at low temperature

Self-regulating heating and self-powered flexibility are pivotal for future wearable devices. However, the low energy-conversion rate of wearable devices at low temperatures limits their application in plateaus and other environments. This study introduces an azopolymer with remarkable semicrystallinity and reversible photoinduced solid-liquid transition ability that is obtained through copolymerization of azobenzene (Azo) monomers and styrene. A composite of one such copolymer with an Azo: styrene molar ratio of 9:1 (copolymer is denoted as PAzo_9:1-co-polystyrene (PS)) and nylon fabrics (NFs) is prepared (composite is denoted as PAzo_9:1-co-PS@NF). PAzo_9:1-co-PS@NF exhibits hydrophobicity and high wear resistance. Moreover, it shows good responsiveness (0.624 s⁻¹) during isomerization under solid ultraviolet (UV) light (365 nm) with an energy density of 70.6 kJ kg⁻¹. In addition, the open-circuit voltage, short-circuit current and quantity values of PAzo_9:1-co-PS@NF exhibit small variations in a temperature range of -20 °C to 25 °C and remain at 170 V, 5 μA, and 62 nC, respectively. Notably, the involved NFs were cut and sewn into gloves to be worn on a human hand model. When the model was exposed to both UV radiation and friction, the temperature of the finger coated with PAzo_9:1-co-PS was approximately 6.0°C higher than that of the other parts. Therefore, developing triboelectric nanogenerators based on the in situ photothermal cycles of Azo in wearable devices is important to develop low-temperature self-regulating heating and self-powered flexible devices for extreme environments.