Oleic acid as a synergistic agent in the formation of kaolinite-mineral oil Pickering emulsions

In this work, we investigated the synergistic effect, stability and interaction mechanisms between kaolinite and oleic acid added in situ and the physically pre-adsorbed in oil-water emulsions. Our motivation here was to prove the claims hypothesized previously by Silva et al. (2018), from studies of our research group, about the in situ cooperative association between kaolinite and the free fatty acids at oil/water interface. Three emulsions were formulated containing mineral oil, water and emulsifiers such as kaolinite, oleic acid or kaolinite-ol (hydrophobized with oleic acid). The samples emulsified by kaolinite and oleic acid, added in situ, showed an increase in the emulsified volume and in the emulsified oil ratio. Oil-in-water emulsions and droplet size ranging between 3.0 μm and 4.8 μm, related to kaolinite concentration, were observed. The emulsified oil fraction of the sonicated samples of kaolinite-ol emulsion was lower than in the emulsions obtained by vortexing, associated to oleic acid desorption. Microscopic images revealed a Pickering effect and partial droplet recovery in all emulsions, suggesting synergistic interaction between kaolinite and oleic acid and better wettability of the particles, resulting in higher emulsified volumes and increased emulsion stability.