Robust and low swelling polyacrylamide/sodium alginate dual-network hydrogels via multiple freezing strategy toward amphibious motion sensors

The swelling and disintegration behavior of conventional hydrogels in liquid environments significantly affects their mechanical and ionic conductive properties, thereby limiting their widespread application in underwater setting. Herein, we propose a multiple freezing (MF) strategy for the construction of polyacrylamide/sodium alginate (PAM/SA) dual-network hydrogels that exhibit excellent anti-swelling properties and high toughness. The MF strategy employs a combination of freeze casting and refreezing to promote a cascading enhancement of polymer network density, resulting in a highly dense polymer network. This dense network structure endows the hydrogel with impressive tensile strength (3.491 MPa), exceptional elongation at break (435.71 %), and high toughness (5.291 MJ m(-)(3)), along with remarkable ionic conductivity (142.75 mS m(-)(1)) and sensitivity (GF = 2.278). These properties enable the hydrogel to function as a flexible sensor capable of detecting various human movement patterns. Its excellent resistance to swelling makes it an ideal material for underwater sensors, effectively monitoring different swimming strokes. This strategy provides a straightforward and effective means to enhance the mechanical strength and adaptability of traditional hydrogels in aquatic environments, demonstrating significant potential for applications in underwater sensing.