Rational Design of a High‐Strength Tough Hydrogel from Fundamental Principles

Abstract Currently, polymer‐based hydrogels have found applications in many fields but are faced with a challenge how to reach an optimum trade‐off between strength and toughness. In this regard, two prototypes (i.e., poly(AAm‐ co ‐AA)/CS‐Fe 3+ and poly(AAm‐ co ‐AA)/PVA‐Fe 3+ double‐network (DN) hydrogels), following the fundamental principles, are developed for the first time through constructing covalent/ionic dual cross‐links in the first networks while inducing polymer entanglement/crystallite‐based hidden chains in the second networks. Through systematic investigation of their comprehensive mechanical properties, the rationality of the proof‐of‐concept strategy is verified but some modifications are needed for further improvement. In summary, the synergy of DN structure and integrated irreversible/reversible dual cross‐links in a sacrificing network can formulate an effective energy‐dissipation system for high toughness, high toughness/strain recoverability, and high antifatigue capability. High‐functionality cross‐links based on polymer crystallites in the second network enhance the strength and elasticity of the as‐prepared hydrogels but destroy the flexibility and softness of the matrix phase, therefore sacrificing their stretchability. For optimal hydrogel design, introducing high‐functionality cross‐links in the matrix network while maintaining its flexibility or constructing hidden chains in the sacrificing network may be an ideal strategy to solve the afore‐mentioned problem.