Water-in-Oil Pickering Emulsions Stabilized by Synergistic Particle-Particle Interactions

Here, we report a novel "double Pickering stabilization" of water-in-oil (W/O) emulsions, where complex formation at the interface between Pickering polyphenol particles adsorbing from the oil side and whey protein microgel (WPM) particles coadsorbing from the aqueous side of the interface is investigated. The interfacial complex formation was strongly dependent on the concentration of WPM particles. At low WPM concentrations, both polyphenol crystals and WPM particles are present at the interface and the water droplets were stabilized through their synergistic action, while at higher concentrations, the WPM particles acted as "colloidal glue" between the water droplets and polyphenol crystals, enhancing the water droplet stability for more than 90 days and prevented coalescence. Via this mechanism, the addition of WPM up to 1 wt % gave a significant improvement in the stability of the W/O emulsions, allowing an increase to a 20 wt % water droplet fraction. The evidence suggests that the complex was probably formed due to electrostatic attraction between oppositely charged polyphenol Pickering particles on the oil side of the interface and WPM Pickering particles mainly on the aqueous side of the interface. Interfacial shear viscosity measurements and monolayer (Langmuir trough) experiments at the air-water interface provided further evidence of this strengthening of the film due to the synergistic particle-particle complex formation at the interface.