Engineering acid-resistant pickering emulsions via sustainable CNC-chitosan synergy: The effect of ionic strength

Cellulose nanocrystals (CNC) are renewable, biocompatible colloids widely used to stabilize Pickering emulsions. However, their strong negative surface charge limits interfacial adsorption, causing poor particle packing, reduced stability, and high sensitivity to acidic or high-ionic-strength environments. Here, we engineer CNC-chitosan binary particles via heteroaggregation to obtain acid-stable Pickering emulsions. We characterized the morphology and hydrophobicity of CNC and binary particles and systematically compared the emulsification efficiency of gel and powder CNC (CNC-G and CNC-P) across rotor-stator, ultrasonication, and high-pressure homogenization. Structural analysis (TEM, XRD, FTIR) revealed that extensive inter-particle hydrogen bonding locks CNC-P into rigid aggregates, contrasting with the flexible, dispersed CNC-G. Emulsion microstructure was analyzed by optical and confocal laser scanning microscopy, and pH effects on emulsions stabilized by pure CNC or binary particles were assessed via droplet size, zeta-potential, emulsifying activity index (EAI), emulsification index (EI), and rheology. Increasing chitosan ratio tuned hydrophobicity and surface charge; at 20% chitosan, charge reversed to positive and contact angles reached ∼100°. Ultrasonication gave the highest EAI for both CNC types. Ionic-strength studies showed that CNC-G stabilized emulsions at 1 wt% CNC and 10 mM NaCl, whereas CNC-P required 2 wt% CNC and 5 mM. Under acidic conditions, cationic binary particles formed stable, well-dispersed, low-viscosity emulsions, providing a sustainable strategy to design pH-responsive, acid-stable Pickering emulsions for food and pharmaceutical applications.