Effect of oil phase on the interfacial behavior and emulsification ability of hydrophobically modified chitosan microgels

The interfacial behaviors of microgels at the oil-water interface were significantly affected by the properties of the oil phase, which in turn influence their emulsification ability. In this study, the effects of oil polarity on the interfacial behaviors of hydrophobic modified chitosan microgels ( h -CSMs) at five typical oil-water interfaces (decane, 1-chlorodecane, decanol, medium-chain triglycerides (MCT), and paraffin) were investigated. The interfacial adsorption results show that h -CSMs can rapidly adsorb onto the selected oil-water interfaces, with the ability to reduce surface tension ( γ ) increased as the polarity of the oil phase increased. The saturation adsorption interfacial pressure ( π ) has a power law index (α) equal to 1.19 with the initial oil-water interfacial tension ( γ ow ) indicating that the h -CSMs are soft particles with interfacial deformability between surfactants and flexible proteins. The h -CSMs formed strong viscoelastic interfacial layers at all of the oil-water interfaces except decanol with the dilatational modulus ( E ) positively correlated to the thickness and amount of adsorbed microgels at the interface. From the interfacial microstructure analysis, weakly polar oils (such as paraffin, n-decane) contributes to the expansion of h -CSMs particles, thereby forming a thicker adsorption layer. The polar oil phase suppresses the excessive expansion of h -CSMs, resulting in a compact and thinnest adsorption layer (such as decanol). Emulsion stability studies showed that the polarity and viscosity of the oil phase, and the interfacial properties of the h -CSM film affect the stability of the emulsions, but the interfacial viscoelasticity dominated. Paraffin emulsions (particularly the high internal phase emulsions, HIPEs) stabilized by h -CSMs exhibit superior storage, mechanical, thermal, and ion stability, but the addition of excessive salt ions will introduce emulsion instability by changing the charge properties and thus the morphology and interaction of the microgels at the interface.