Influence of non-ionic surfactant addition on the stability and rheology of particle-stabilized emulsions

Hypothesis: Nanoparticle wettability is expected to influence the surfactant adsorption onto an oil-water interface, which in turn would affect the structure and rheology of Pickering emulsions. Experiments: We investigated the influence of non-ionic surfactant (Span 80) addition to Pickering emulsions stabilized by either partially hydrophobic (Aerosil R711) or hydrophobic (Aerosil R812S) fumed silica particles. Findings: The addition of a non-ionic surfactant to emulsions stabilized by hydrophobic fumed silica particles decreased the droplet size of emulsions unlike emulsions stabilized by partially hydrophobic fumed silica particles. Even under low shear conditions, the addition of a non-ionic surfactant displaced the hydrophobic fumed silica particles from the oil-water interface unlike partially hydrophobic fumed silica particles. Our results suggested that the displacement of hydrophobic fumed silica particles by the addition of a non-ionic surfactant was not due to the change in nanoparticle wettability by surfactant adsorption onto the surface of fumed silica particles. Viscosity of emulsions stabilized by partially hydrophobic fumed silica particles decreased upon the addition of a non-ionic surfactant. In contrast, the viscosity of emulsions stabilized by hydrophobic fumed silica particles increased upon the addition of a non-ionic surfactant. Depending on the nanoparticle wettability, the addition of a non-ionic surfactant influenced the elastic and viscous properties of Pickering emulsions.