Superparamagnetic nanoclusters coated with oleic acid bilayers for stabilization of emulsions of water and oil at low concentration

Emulsions of water and dodecane with drop sizes down to 1 μm were stabilized with 30–100 nm interfacially active nanoclusters of sub-15 nm iron oxide primary particles at an extremely low loading of 0.14 wt.%. The nanoclusters, coated with a bilayer of oleic acid, formed stable dispersions in water at pH 7–10. The phase behavior and droplet morphologies of the emulsions of water and dodecane were tuned with pH. The oil/water emulsions at pH 9–10 were converted to middle phase emulsions at pH 6–7 and water/oil emulsions as the pH was further lowered. The magnetization per gram of Fe is similar for the nanoclusters and the primary particles, indicating the spacing between the particles is sufficient to avoid magnetic coupling. The larger volume of nanoclusters relative to the individual primary particles is beneficial for magnetomotive sensing applications including imaging of oil reservoirs, as it increases the force on the particles for a given magnetic field.