Mechanistic insights into the formation and stability of self‐assembled chito‐oligosaccharide/fucoidan polyelectrolyte complexes

Abstract This study systematically evaluated the effects of compositional ratios and concentrations on the structural and functional properties of chito‐oligosaccharide (COS) and fucoidan (FUC) polyelectrolyte complexes (PECs). Comprehensive characterization via particle size analyzer, ζ‐potential measurements, Fourier transform infrared spectroscopy, AFM and TEM revealed formulation‐dependent self‐assembly mechanisms. The results demonstrated that PEC formation and properties exhibited high dependence on both the polysaccharide mixing ratio and concentration. At 1 mg mL −1 , a lower COS content (COS:FUC ratios of 2:8 to 6:4) yielded smaller particle sizes (e.g. 645.3 nm at 6:4), higher ζ‐potentials, enhanced colloidal stability and improved ion dispersion, whereas COS‐rich formulations favored aggregation. The 6:4 ratio exhibited optimal performance, with 86.15% yield and stable behavior. Solution stability inversely correlated with concentration, improving under dilute conditions. Isothermal titration calorimetry analysis revealed a four‐stage COS–FUC binding process: initial rapid exothermic release, enthalpy‐driven chain rearrangement, gradual energy dissipation, and equilibrium stabilization. Structural analyses confirmed that spherical PEC morphologies were governed by electrostatic interactions and hydrogen bonding. These findings establish quantitative structure–property relationships for tailoring COS–FUC PECs in food‐grade delivery systems and functional coatings, advancing the rational design of sustainable polysaccharide‐based materials. © 2026 Society of Chemical Industry.