Anti-freezing conductive zwitterionic composite hydrogels for stable multifunctional sensors

Zwitterionic conductive hydrogels have shown potential application in wearable strain and pressure sensors. However, there are still fundamental challenges to achieve zwitterionic hydrogels with excellent mechanical properties, able to keep flexibility at sub-zero temperatures. To overcome these limitations, a zwitterionic conductive hydrogel was fabricated in this work by in-situ polymerization of aniline (ANI) monomer in a copolymer of sulfobetaine methacrylate (SBMA) and acrylic acid (AA) matrix. The obtained hydrogel possesses outstanding anti-freezing performance (without obvious loss of stretchability at −18 °C) and water-retaining properties, due to the introduction of LiCl on the zwitterionic polymer matrix. The synergy of chemical and physical crosslinking between poly (SBMA-co-AA) and polyaniline (PANI) networks enhance the mechanical performance of the zwitterionic hydrogel, that exhibits a fracture tensile strength of 470 kPa, and a fracture strain up to 600 %. Additionally, the integration of PANI confers stable conductivity (2.23 S m−1, maintained at 1.89 S m−1 even at −18 °C), high sensitivity (GF = 1.74), and short response and recovery times (223 ms and 191 ms, respectively). The hydrogel can be applied as a flexible sensor to accurately detect various human motions. This work provides a feasible strategy for developing wearable multifunctional sensors in a wide working temperature range.