Magnetic pickering emulsions stabilized by Fe 3O 4 nanoparticles

Superparamagnetic Fe3O4 nanoparticles prepared by a classical coprecipitation method were used as the stabilizer to prepare magnetic Pickering emulsions, and the effects of particle concentration, oil/water volume ratio, and oil polarity on the type, stability, composition, and morphology of these functional emulsions were investigated. The three-phase contact angle (θow) of the Fe3O4 nanoparticles at the oil−water interface was evaluated using the Washburn method, and the results showed that for nonpolar and weakly polar oils of dodecane and silicone, θow is close to 90°, whereas for strongly polar oils of butyl butyrate and 1-decanol, θow is far below 90°. Inherently hydrophilic Fe3O4 nanoparticles can be used to prepare stable dodecane−water and silicone−water emulsions, but they cannot stabilize butyl butyrate−water and decanol−water mixtures with macroscopic phase separation occurring, which is in good agreement with the contact angle data. Emulsions are of the oil-in-water type for both dodecane and silicone oil, and the average droplet size increases with an increase in the oil volume fraction. For stable emulsions, not all of the particles are adsorbed to drop interfaces; the fraction adsorbed decreases with an increase in the initial oil volume fraction. Changes in the particle concentration have no obvious influence on the stability of these emulsions, even though the droplet size decreases with concentration.