Soft, Strong, and Tough Hydrogel Fibers with Rapid Strain-Stiffening Behavior via the Synergy of Oriented-Coiled Network and Salt-Regulation

Hydrogel fibers have been widely used in flexible electronics owing to their flexibility, ionic conductibility, and weavability. However, hydrogel fibers exhibit a typical trade-off between strength and flexibility (strength-modulus conflict), which is attributed to enhanced intra- or inter-molecular chain interactions of hydrogel fibers, usually cause a simultaneous increase in their strength and modulus. Herein, a drawing-partial fixing-relaxation (DPR) strategy is proposed to overcome the strength-modulus conflict of hydrogel fibers. And the DPR strategy is synergized with the salt-regulated toughening strategy to fabricate soft, strong, and tough hydrogel fibers with a network composed of partially-oriented coiled molecular chains (oriented-coiled network). Benefiting from the oriented-coiled network and abundant energy dissipation units (e.g., ionic coordination and crystalline domains), the obtained hydrogel fiber exhibits a high strength/modulus ratio (19.19 ± 5.27), excellent toughness (138.11 ± 8.09 MJ m^-3), and rapid strain-stiffening behavior. In addition, hydrogel fibers synergistically prepared with DPR and salt-regulated strategies allow to customize their elastic modulus (0.51 ± 0.15 to 5.69 ± 0.69 MPa), strength (15.67 ± 0.2 to 79.09 ± 2.33 MPa), and strain-stiffening ability (4.32 ± 0.25 to 41.78 ± 4.43) through process adjusting and salt regulating. Notably, the DPR strategy can be generalized to other systems (such as double network and copolymer systems) to improve their strength/modulus ratios and strain-stiffening abilities. Furthermore, the obtained hydrogel fibers are applied to vibration damping and flexible sensors, demonstrating promising vibration damping as well as stable monitoring of deformation, impact, and vibration. This work provides a novel approach to fabricate soft, strong, and tough hydrogel fibers for flexible electronics.