Highly-sensitive, anti-freezing, recyclable chitosan quaternary ammonium salt hydrogel constructed by piezoelectric...

Chitosan-based piezoresistive conductive hydrogels are gaining popularity in wearable sensors. However, the practical application of sensors is still restricted by their sensitivity and anti-freezing properties. The optimal design of hydrogels is expected to solve the challenges. Herein, a double-network hydrogel (PHPP-300) that integrates piezo-resistivity sensing enhancement and anti-freezing ability improvement is reported by introducing the piezoelectric dipole effect of poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) and using DMSO as an antifreezing agent. In detail, a physical cross-linked network is constructed by poly(vinyl alcohol) (PVA), chitosan quaternary ammonium salt (HACC) and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) through dipole interaction and hydrogen bonding. The hydrogel exhibits high stretchability (tensile strength: 7.5 MPa, elongation at break: 467%). It can maintain flexibility at -60 °C. Notably, PVDF-TrFE endows the PEDOT: PSS hydrogel with good response ability by regulating the internal electron transport path to obtain a high gauge factor sensor (GF = 43.1, R² = 0.96). PHPP-300 retains its mechanical and sensing properties after the recycling process at 70 °C for 4 h. Furthermore, the designed wearable gloves based on PHPP-300 hydrogel can control the unman car at -40 °C. This hydrogel combines a fully physical and recyclable double-network with piezoelectric-regulated charge transport and antifreezing capability compared with reported chitosan-based conductive hydrogels. This work presents an effective constructed strategy for tough, low-temperature sensitive and recyclable hydrogel sensors based on chitosan quaternary ammonium salt.