Strong Tough Conductive Hydrogels via the Synergy of Ion-Induced Cross-Linking and Salting-Out

Ion is one of the most common additives that can impart electrical conductivity to insulating hydrogels. The concurrent toughening effect of ions, however, is often neglected. This work reports the extreme toughening of hydrogels via the synergistic effect of cations and anions, without the need for specific structure design or adding other reinforcements. The strategy is to equilibrate a physical double network hydrogel consisting of both multivalent cation- and kosmotropic anion-sensitive polymers in specific salt solutions that can induce cross-linking and salting-out simultaneously. Both effects are proven positive to boost the mechanical performance and electrical conductivity of the original weak gel, and result in a tough conductive gel with exceptional physical properties, achieving significant enhancements in fracture stress, fracture energy, and ionic conductivity by up to 530-, 1100-, and 4.9-folds, respectively. The optimal fracture stress and toughness reach approximately 15 MPa and 39 kJ m(-2), exceeding most state-of-the-art tough conductive hydrogels. Meanwhile, a satisfactory ionic conductivity of 1.5 S m(-1) is attained. The presented simple strategy is also found generalizable to other salt ions and polymers, which is expected to expand the applicability of hydrogels to conditions involving demanding mechanical durability.