Counterion-Regulated Coordination in Chitosan Hydrogels: Structure, Ionic Transport, and Electroluminescent Function

Understanding how ionic coordination governs structure–property relationships in biopolymer hydrogels remains a significant challenge in the design of functional soft materials. Here, we introduce a counterion-regulated coordination strategy to tailor the architecture and ionic transport of chitosan/poly(ethylene glycol) diglycidyl ether (CS/PEGDE) dual-network hydrogels coordinated with Al 3+ (0.5–1.5 M). By varying the counterion identity between chloride (AlCl 3, A2 ) and sulfate (Al 2 (SO 4 ) 3, A3 ), distinct coordination environments are generated without altering the polymer backbone or covalent cross-linking chemistry. Comprehensive structural, spectroscopic, thermal, mechanical, and electrochemical characterization reveals that sulfate counterions promote stronger, more interconnected coordination domains, yielding denser hydrogels with higher thermal stability (DSC ≈ 170 °C), improved tensile strength, enhanced ionic conductivity, reduced charge-transfer resistance, and increased dielectric response. In contrast, chloride counterions generate more dynamic coordination environments with greater chain mobility, lower thermal transition temperatures (≈132 °C), and a nonmonotonic mechanical response. Quantitative electrochemical analysis further supports the presence of more efficient ionic transport in the sulfate-regulated hydrogel. As a functional demonstration, the hydrogels were integrated into flexible electroluminescent devices, exhibiting stable light emission under large mechanical deformation. This work establishes counterion-regulated coordination as an effective strategy to tune dynamic interactions and electrochemical performance in biomacromolecular hydrogels, providing new insights into the rational design of ionically cross-linked soft materials.