title: Chitosan-Based Conventional and Pickering Emulsions with Long-Term Stability.
abstract: Chitosan-based conventional and Pickering oil-in-water (O/W) emulsions with very fine droplet size (volume average diameter, dv, as low as 1.7 μm) and long-term stability (up to 5 months) were ultrasonically generated at different pH values without the addition of any surfactant or cross-linking agent. The ultrasonication treatment was found to break and disperse chitosan agglomerates effectively (particularly at pH ≥ 4.5) and also reduce the chitosan molecular weight, benefiting its emulsification properties. The emulsion stability and emulsion type could be controlled by chitosan solution pH. Increasing pH from 3.5 to 5.5 led to the formation of conventional emulsions with decreasing droplet size (dv from 14 to 2.1 μm) and increasing emulsion stability (from a few days to 2 months). These results can be explained by the increase of dynamic interfacial pressure, which results from the conformation transition of chitosan molecules from an extended state to a more flexible structure as pH increases. At pH = 6.5 (the acid dissociation constant (pKa) of chitosan), the chitosan molecules self-assembled into well-dispersed nanoparticles (dv = 82.1 nm) with the assistance of ultrasonication, which resulted in a Pickering emulsion with the smallest droplet size (dv = 1.7 μm) and highest long-term stability (up to 5 months) because of the presence of chitosan solid nanoparticles at the oil/water interface. The key originality of this study is the elucidation of the role of pH in the formation of conventional and Pickering chitosan-based O/W emulsions with the assistance of ultrasonication. Our results suggest that chitosan possesses great potential to be used as an effective pH-controlled emulsifier and stabilizer without the need of other additives.
authors.affiliation: Department of Chemical Engineering, CREPEC, Polytechnique Montréal , PO Box 6079, Station Centre-Ville, Montréal, QC Canada H3C 3A7.
authors.forename: Xiao-Yan
authors.initials: XY
authors.lastname: Wang
authors.affiliation: Department of Chemical Engineering, CREPEC, Polytechnique Montréal , PO Box 6079, Station Centre-Ville, Montréal, QC Canada H3C 3A7.
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Heuzey
mesh_terms: D000327:Adsorption; D048271:Chitosan / Q000737:chemistry*; D004355:Drug Stability; D004655:Emulsions / Q000737:chemistry*; D008968:Molecular Conformation; D008970:Molecular Weight; D010316:Particle Size; D013010:Sonication; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D004655:Emulsions; D014867:Water; D048271:Chitosan