Piezoresistive Sensor Based on Porous Sponge with Superhydrophobic and Flame Retardant Properties for Motion Monitoring and Fire Alarm.

Polyurethane sponge is frequently selected as a substrate material for constructing flexible compressible sensors due to its excellent resilience and compressibility. However, being highly hydrophilic and flammable, it not only narrows the range of use of the sensor but also poses a great potential threat to human safety. In this paper, a conductive flexible piezoresistive sensor (CHAP-PU) with superhydrophobicity and high flame retardancy was prepared by a simple dip-coating method using A-CNTs/HGM/ADP coatings deposited on the surface of a sponge skeleton and modified with polydimethylsiloxane. With great sensitivity and durability (>3000 cycles) as well as fast response/recovery time (152 ms/178 ms), the sensor is capable of monitoring human movement as a wearable device. The modified material surface has a hydrophobicity angle of 153°, which provides significant self-cleaning and weather resistance. Furthermore, the CHAP-PU sensor is able to respond stably to underwater movements. Importantly, when the sponge was directly exposed to an open flame, no flame spreading or dripping of molten material was detected, indicating excellent flame retardancy. Meanwhile, CHAP-PU was also equipped as a smart fire alarm system, and the results showed that an alarm signal was triggered within 2 s under flame erosion. Therefore, the flame-retardant superhydrophobic CHAP-PU sponge-based sensor shows great potential for human motion detection and fire alarm applications.