Conductive\nHydrogels with Ultrastretchability and\nAdhesiveness for Flame- and Cold-Tolerant Strain Sensors

Abstract

Hydrogel\nstrain sensors with extreme temperature tolerance have\nrecently gained great attention. However, the sensing ability of these\nhydrogel strain sensors changes with temperature, resulting in the\nvariety of output signals that causes signal distortion. In this study,\ndouble-network hydrogels comprising SiO₂ nanoparticles\ncomposed of polyacrylamide and phytic acid-doped polypyrrole were\nprepared and applied on strain sensors with a wide sensing range,\nhigh adhesiveness, and invariable strain sensitivity under flame and\ncold environments. The hydrogels had stable conductivity, excellent\nadhesive strength of up to 79.7 kPa on various substrates, and high\nelongation of up to 1896% at subzero temperature and after heating.\nThey also exhibited effective flame retardancy with low surface temperature\n(71.2 °C) after 1200 s of heating (200 °C) and antifreezing\nproperties at a low temperature of −20 °C. Remarkably,\neven under cold temperature and heat treatment, the hydrogel-based\nstrain sensor displayed consistent sensing behaviors in detecting\nhuman motions with a broad strain range (up to 500%) and steady gauge\nfactor (GF, ∼2.90). Therefore, this work paves the way for\nthe applications of hydrogel sensors in robotic skin, human–mechanical\ninterfaces, and health monitoring devices under harsh operating environments.