Structure–property relationships in ternary κ-carrageenan/chitosan/PVA hydrogel membranes tuned by polyelectrolyte complex formation

Composition-dependent polyelectrolyte complex (PEC) formation was investigated in ternary κ -carrageenan/chitosan/poly(vinyl alcohol) ( κ -CRG/CS/PVA) hydrogel membranes over a broad κ -CRG:CS/PVA compositional range. Systematic variation of composition altered intermolecular interactions and produced changes in heterogeneous network organization. Optical microscopy revealed composition-dependent fibrillar heterogeneity, particularly in the κ -CRG-rich membranes, consistent with heterogeneous polymer organization. The precursor mixtures exhibited a non-monotonic viscoelastic response that could not be fully explained by differences in total polymer concentration, indicating composition-dependent organization prior to membrane formation. The resulting differences in network organization were subsequently reflected in the structural order, surface roughness, wettability, swelling, thermal behavior, and hydrated mechanical response of the cast membranes. Among the investigated compositions, the 9:1 membrane exhibited the most distinctive behavior, combining the lowest equilibrium swelling (111.0 ± 10.8%) with a markedly higher hydrated elastic modulus (8.01 ± 0.96 MPa) and the highest diazinon adsorption capacity (3.49 ± 0.47 mg/g). Diazinon adsorption did not follow the swelling trend, indicating that network hydration alone does not determine molecular uptake and that composition-dependent network organization and adsorption-site accessibility also contribute. Taken together, the results establish composition as an effective design variable for regulating PEC-related network organization and provide a composition-network organization–property framework for tailoring κ -CRG/CS/PVA hydrogel membranes for aqueous-phase sorption and separation.