Ion-Triggered Reconfigurable Hydrogel with Salt-Enhanced Mechanical and Swelling Properties via Network Topological Adaptation

Hydrogels typically deteriorate in high salinity due to electrostatic screening and solvent-quality loss. Here, we report a double network hydrogel, composed of poly(AMPS)(2-acrylamido-2-methylpropane sulfonic acid) and zwitterionic AM-SBVI (acrylamide-sulfobetaine vinylimidazole) that strengthens while swelling in brine. Upon salt exposure, the network undergoes ion-triggered topological reconfiguration, the intrachain zwitterionic loops open and re-form as inter-network SBVI ⁺ -AMPS ⁻ bridges, which yields a higher effective bridge density v _e , at lower polymer fraction(Φ). The hydrogel demonstrates a 3.4-fold increase in tensile strength and a 2.1-fold enhancement in equilibrium swelling ratio in 200 g/L NaCl compared to deionized water. Small-angle X-ray scattering (SAXS) and X-ray photoelectron spectroscopy (XPS) confirm the ion-mediated decoupling of crosslinking domains and redistribution of charge density. Moreover, simulation calculation suggests a more strong interaction between SBVI and AMPS under high salinity water. Coreflooding experiment demonstrates robust injectability and flow-resistance characteristics under high salinity porous rock. A deep analysis concerts swelling/rheology into three descriptors, v ₑ, χ (Flory-Rehner inversion), and f _loop (loop fraction from bridge capacity). We find that salt contents raise and depress f _loop toward zero. This, the elastic cost term, F _el increases but is compensated by F _assoc (stabilization from loop to bridge), while F _diss from Donnan partioning is small. F _mix that related to χ shifts quite small indicated a strong interaction between the hydrogel with brine. This quantitative mechanism explains the simultaneous gains in swelling and modulus and provides rational design rules to engineer salt-adaptive hydrogels for subsurface and biointerfaces.