Oil-in-water Pickering emulsions stabilized by phyllosilicates at high solid content

Abstract : The present study aims at investigating the preparation and characterization of oil-in-water (O/W) Pickering emulsions stabilized using three different phyllosilicates: kaolin, halloysite, and palygorskite, and at high solid content (15 wt.% in the aqueous phase). Stable O/W emulsions could be obtained with no additional surfactant or surface treatment. The maximal oil fraction that could be introduced without phase separation was determined. The resulting oil/water ratios of 0.32, 0.44 and 0.60 were found for kaolin, halloysite and palygorskite, respectively. The O/W character of the three emulsions was confirmed by a simple “droplet test” and by confocal microscopy, which confirmed the positioning of the clay particles at the oil/water interface. These three phyllosilicates led to a limited coalescence mechanism that promoted the long-term stability of the Pickering emulsions. The rheological behavior of these emulsions was studied and showed that halloysite led to a more rigid structure. This trend could be justified by the formation of a strong network of clay particles due to strong surface interactions combined with an elongated particle shape.