Robust Polypyrrole@Halloysite Nanotube-Coated Polyurethane Sponge as Multifunctional Flexible Sensors

Polyurethane (PU) sponge with high elasticity and reproducibility shows promising application in flexible electronic devices. However, the poor conductivity and high flammability limit its application field, which also pose a potential threat to human health. Here, a flexible sponge sensor based on PU and polypyrrole-wrapped halloysite nanotubes (PPy@HNTs) was successfully fabricated by the dip coating technology. The PPy-modified HNTs showed strong binding ability on the PU sponge by employing N,N-dimethylformamide (DMF) as an interfacial solvent. PPy@HNTs can well adhere on the surface of the PU sponge, which endow excellent structural stability to the flexible sponge sensor after 5000 cycles. The response and recovery times during the sensitivity experiment of the flexible sponge sensor are 265.63 and 265.62 ms, respectively. The flexible sponge sensor can effectively detect various physical activities, such as walking, facial expression, and gesture. It can be used as an analytical balance for quality monitoring. Moreover, the flexible sponge sensor exhibits excellent photothermal performance, which is reflected in the good relationship between resistance change and laser irradiation time as well as power intensity. The coating of PPy@HNTs also significantly improved the flame retardancy of the PU sponge. This work developed a mild, high-efficiency, and simple preparation method of flexible sponge sensors, and the prepared sensor displayed multifunctional applications such as biological detection and electronic balances.