Enhancing stability of Pickering emulsions: Insights into the interfacial dynamics of Zein-MCT composite nanoparticles

Abstract

The interfacial adsorption properties of colloidal particles were critical to the formation and stability of Pickering emulsions. This study aimed to improve the surface hydrophobicity, adsorption properties of Zein nanoparticles (ZN) by using the hydrophobic substance Medium-chain triglyceride (MCT) to form hybrid nanoparticles (ZMN). We investigated the impact of varying Zein/MCT ratios on the interfacial stabilization mechanism of Pickering emulsions and deciphered the relationship between adsorption properties, the rheological behavior of interfacial layer, and emulsion stability. Results revealed that the surface hydrophobicity of nanoparticles affected their adsorption properties as well as the rheological behavior of the composite interface. Specifically, an increase in the Zein/MCT ratio promoted the exposure of hydrophobic groups, increased the surface hydrophobicity of ZMN. This further led to an enhanced diffusion ZMN from the aqueous phase to the interface (Kdiff increased from 0.033 mNm−1s−0.5 to 0.095 mNm−1s−0.5) and the rate of rearrangement at the interface (KR increased from −0.016 mNm−1s−0.5 to −0.009 mNm−1s−0.5) which resulted in rapid adsorption and densely accumulation of ZMN at the interface. Furthermore, the adsorption properties of the nanoparticles directly influenced the viscoelastic and strain properties of the interfacial layer. The interfacial layer composed of ZMN exhibited enhanced viscoelasticity, increasing from 4 mN/m to 7 mN/m at low frequencies and from 6.8 mN/m to 12.5 mN/m at high frequencies. It also exhibited lower viscous dissipation and a stronger deformation response under varying external pressures. As a consequence, the rate and extent of droplet aggregation in ZMN stabilized emulsions (ZMNPEs) were reduced, attributing to the high viscoelasticity as well as the strong strain response of the interfacial layer. This research not only introduces a novel strategy to enhance the stability of Pickering emulsions using Zein-MCT composite nanoparticles, but also deepens our understanding of the interplay between particle adsorption properties, interfacial rheology, and emulsion stability.