Synergistic rigid-flexible dual-network hydrogel with robust absorbency and anti-freezing property

The development of materials with high water absorption, long-lasting water retention, and frost resistance is of great significance for the development of arid, semi-arid, and cold regions. This study utilized acrylic acid (AA), acrylamide (AM), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and N , N ′-methylenebisacrylamide (MBA) as precursors to construct a covalently crosslinked rigid network through free radical polymerization, while sodium carboxymethyl cellulose (CMC) and Ca 2+ ions were introduced to fabricate the flexible network via non-covalent interactions, yielding a PAA-AM-AMPS/CMC dual-network hydrogel with a three-dimensional architecture. The resultant hydrogel exhibited a water absorption capacity of 1435 g/g in aqueous solution, and the soil combined with 1 wt% hydrogel attained a remarkable water holding capacity of 156 %. It maintained 25 % moisture after 20 days and exhibited only a 23 % reduction in water retention after fifteen cycles, so illustrating exceptional water retention capabilities. Moreover, the compact dual-network structure endowed the hydrogel with a stress of 0.248 MPa and a fracture elongation of 1280 %, concurrently reducing the freezing point to −33.15 °C, significantly enhanced the hydrogel's mechanical properties and ultra-freeze resistance. Soil combined with 15 % hydrogel exhibited a freezing point decreased to −13.03 °C and maintained 70.16 % unfrozen water following freezing at −20 °C. Thus, the PAA-AM-AMPS/CMC hydrogel demonstrates exceptional capabilities in water absorption, soil water retention, and freeze resistance, which has considerable implications for efficient water resource management under extreme conditions.