Sulfuric acid-immersed hydrogels composed of polyacrylic acid and aramid nanofiber for enhanced mechanical properties

• The synergistic mechanical enhancement strategy was developed by using sulfuric acid and aramid nanofibers. • Sulfuric acid treatment enhances both strength and elongation simultaneously. • Sulfuric acid-immersed hydrogels composed of polyacrylic acid and aramid nanofiber possesses cyclic self-reinforcing and low-temperature tolerance properties. Overcoming the inherent mechanical limitations of polyacrylic acid (PAA) hydrogels (low strength and toughness) requires innovative strategies. This study introduces a novel synergistic approach combining aramid nanofiber (ANF) reinforcement with sulfuric acid (SA) immersion. By immersing ANF/PAA composite hydrogels (ANF-gel) in SA solution, we fabricate SA-treated gels (SA-gel) where SA dynamically reprograms the network: protonating carboxyl groups eliminates electrostatic repulsion, contracts PAA chains, and crucially, establishes a high-density, dynamic hydrogen bond network with ANF surface amide bonds. This synergistic mechanism concurrently achieves exceptional strength (0.83 MPa) and toughness (2.88 MJ·m− 3 ). Remarkably, the dynamic nature of this network enables unprecedented cyclic self-reinforcement, with stress progressively increasing to 2 MPa during repeated strain cycling due to hydrogen bond rearrangement and ANF alignment. Furthermore, SA robustly binds water molecules, conferring outstanding flexibility retention even at extreme temperatures (−50 °C). This SA immersion strategy offers a versatile and effective pathway for engineering high-performance, multifunctional hydrogels.