(615b) The Influence of Nanoparticle Morphology on Surfactant-Nanoparticle Interactions in Emulsions

Surfactant-nanoparticle interactions play a critical role in determining the stability of emulsions. Our objective is to elucidate the impact of particle morphology and wettability on surfactant-nanoparticle interactions at fluid-fluid interfaces. Fumed silica nanoparticles and ellipsoidal nanoparticles having the same hydrodynamic diameters were used to quantify the impact of particle morphology on the droplet size, emulsion stability, and the rheology of Pickering emulsions. Three silica nanoparticles of different wettability were used to determine the impact of wettability on surfactant-nanoparticle interactions. Sorbitan monooleate (Span 80), a non-ionic surfactant, was used to probe the surfactant-nanoparticle interactions at fluid-fluid interfaces. By probing the surfactant-fumed silica nanoparticle interactions, we showed that surfactant stabilized water-in-cyclohexane emulsions can be destabilized depending on the nanoparticle wettability and the mode of nanoparticle addition. Water-in-cyclohexane were destabilized when partially hydrophobic fumed nanoparticles were added to the surfactant-stabilized emulsion after emulsion formation (post-mixing). Water-in-oil emulsions were not destabilized upon post-mixing hydrophobic fumed nanoparticles due to weak hydrophobic interactions between surfactants and hydrophobic nanoparticles. For a fixed concentration of fumed silica nanoparticles of specific wettability, changing the mode of nanoparticle addition altered the flow behavior and the network strength of surfactant stabilized water-in-cyclohexane emulsions.