Super-Robust and Heat-Resistant Crystalline Hydrogels via Hofmeister-Tuned Annealing

Achieving the combined requirements of high toughness and heat resistance in the thermal environment remains a fundamental challenge for hydrogels. Crystalline hydrogels stand out among hydrogels due to their excellent mechanical properties. However, the solvent environment of hydrogels exacerbates the metastability of crystalline domains functioning as cross-linking nodes, which severely limits the development and safe service of crystalline hydrogels with high mechanical and heat-resistant properties. Here, a stabilizing crystalline domain strategy is proposed to construct super-robust and heat-resistant crystalline hydrogels via in situ Hofmeister-tuned annealing. Hofmeister-tuned annealing simultaneously enhances the thermodynamic and kinetic stability of crystalline domains via lowering system's free energy of crystalline domains and constructing strong hydrogen-bonding high-energy barriers in amorphous regions, respectively. Super-robust crystalline hydrogels exhibit a super-high tensile strength of 23.82 MPa and a fracture energy of 47.65 kJ m^-2. More stable crystalline domains provide a crosslinking method to balance the conflict between stiffness and toughness of hydrogels. As hydrogen bond domains, more stable crystalline domains enable crystalline hydrogels to overcome the heat-resistance limitation of physical hydrogels at 100°C. The stabilizing crystalline domain strategy provides a pathway to construct super-robust and heat-resistant crystalline hydrogels via Hofmeister-tuned annealing, thereby significantly broadening their application boundaries in harsh environments.