Hydroxypropyl-phenyltriazole-functionalized chitosan as an adaptive amphiphilic emulsifier: Interfacial stabilization, rheology, and antioxidant activity.

Chitosan (CS) is an attractive bio-based macromolecule for emulsion stabilization, but its strong hydrophilicity, pH-dependent solubility, and limited oil-water interfacial affinity restrict its performance as a robust polymeric emulsifier. Herein, hydroxypropyl-phenyltriazole-functionalized chitosan (CS-HP-PhTrz) was synthesized via CuAAC click chemistry as an amphiphilic CS derivative with improved interfacial adaptability and antioxidant functionality. Successful functionalization was supported by FTIR, UV-Vis, 1H NMR, XRD, TGA, SEM-EDX, and XPS analyses, with an estimated degree of substitution of 13.6% based on 1H NMR integration of the triazole Hₐ and chitosan H-2 proton signals and no detectable Cu 2p signal in the XPS survey spectrum after purification. Compared with native CS, CS-HP-PhTrz exhibited higher initial hydrophobicity, rapid hydration-induced wettability transition, and retained positive surface charge, indicating dynamically amphiphilic behavior favorable for oil-water interfacial stabilization. Response surface methodology was used to evaluate the effects of emulsifier concentration, oil fraction, and pH on creaming behavior. Native CS showed a restricted formulation window and failed under selected high-oil/high-emulsifier conditions, whereas CS-HP-PhTrz maintained emulsion-forming ability over a broader region and produced near-zero creaming under selected conditions. Rheological analysis revealed elastic-dominant, shear-thinning emulsions, with CS-HP-PhTrz forming a softer and more flowable viscoelastic network than native CS. CS-HP-PhTrz also showed enhanced ABTS radical-scavenging activity, reaching 48.46 ± 1.63%. DFT/COSMO analyses revealed spatially separated polar and hydrophobic domains. A preliminary A549-cell MTT assessment was also conducted, but vehicle-associated effects limited material-specific cytotoxicity interpretation. These results indicate that phenyltriazole functionalization converts chitosan into a multifunctional biomacromolecular emulsifier for sustainable emulsion systems.