Locking aggregation states in tough hydrogels through protective domain formation

Tough hydrogels based on physical crosslinking have attracted tremendous attention due to their excellent mechanical properties achieved through controlled polymer chain aggregation via various processing methods. However, the reversible nature of these physical interactions leads to severe mechanical degradation in aqueous environments, where water molecules competitively disrupt hydrogen bonds and dissolve aggregated structures, fundamentally limiting their practical applications. Herein, we propose a strategy to construct protective domains around physical crosslinks that effectively stabilize the network while preserving energy dissipation capabilities. Using poly(vinyl alcohol) (PVA) as a model system, we implement this design through sequential dehydration-induced crystallization and homogeneous free-radical crosslinking (FRC). The resulting protective domains—chemically-crosslinked loose aggregates surrounding crystallites—serve dual functions: shielding physical crosslinks from solvent-induced disruption and storing hidden chain length that enhances extensibility during deformation. Compared to unprotected physically crosslinked hydrogels, this strategy achieves 2.4-fold enhancement in elastic modulus, 2.1-fold increase in breaking strain, and 4.8-fold improvement in toughness, while dramatically improving environmental stability--the mechanical strength retention increases from ∼ 20 % to > 80 % after aqueous immersion, with volume expansion reduced from typical 20–30 % to less than 5 %. Microstructural characterization confirms the coexistence of protected crystallites and loose aggregates. The hydrogel is successfully employed as an electrolyte to construct zinc-ion batteries that feature superior cycling performance, enabled by the exceptional environmental stability and strong structural endurance of the hydrogel. This strategy proves generalizable to various physically crosslinked systems, offering a universal design principle for creating mechanically robust and environmentally stable hydrogels.