Superior Impact-Resistant Composite Hydrogels Through an Ionic Coupling Strategy.

Impact resistance emerges from the coupling of strong load-bearing networks and dynamic interfacial interactions that enable effective stress transfer and energy dissipation. Although hydrogels are promising candidates for impact-resistant soft materials, it remains challenging to reinforce both networks and interfaces simultaneously in hydrogels, which limits their performance under high strain-rate loading. To overcome this limitation, we develop a composite hydrogel comprised of a poly(vinyl alcohol) (PVA) matrix reinforced with chitosan-sodium alginate nanofibers (CSNFs), using sodium citrate as a multifunctional ionic coupler that (i) strengthens the PVA matrix via the Hofmeister effect, (ii) reinforces the CSNF network through desolvation and electrostatic crosslinking, and (iii) improves their fiber-matrix interfaces, enabling efficient stress transfer and energy dissipation through the integrated composite network and layered microstructure. The composite hydrogel achieves superior impact resistance relative to high-performance solid polymers, with an impact strength of 426.7 MPa and toughness of 106.4 MJ m- 3 at 7000 s- 1, while retaining excellent tensile properties (tensile strength: 54.2 MPa; fracture strain: 590%). By molecular-level experimental and simulation analyses, this work establishes ionic coupling as a facile yet effective strategy for achieving composite hydrogels with extreme impact resistance, broadening the potential of soft materials in impact protection, damping, and energy absorption.