Demulsification of Pickering Emulsions by Chemical Dissolution of Stabilizers

Demulsification of particle-stabilized oil-in-water emulsions is crucial in diverse fields such as treatment of produce water, recovery of valuable products of Pickering emulsion catalysis, and so on. In this work, we investigated a facile method for destabilizing emulsions by dissolving stabilizer particles by the introduction of acid or base. Nanoellipsoidal hematite-stabilized decane-in-water emulsions are destabilized by dissolving hematite with oxalic or hydrochloric acid in situ. Time required for complete demulsification decreased as the acid concentration is increased. The demulsification time is typically on the order of a few hours for the chosen protocol. Similarly, the silica-stabilized decane-water emulsion is demulsified by the addition of aqueous sodium hydroxide. Demulsification kinetics is presented as the temporal change of the emulsion volume with time. Emulsion volume decreases in two stages: an initial slow decrease followed by an exponential decrease. Scanning electron microscopy analysis shows that the stabilizing particles are completely dissolved and recrystallized as salts of respective kinds. An estimate of the desorption free energy suggests that particle size should be reduced to a few nanometers for inducing destabilization. This work describes a facile method to destabilize oil-in-water emulsion, and it can be generalized to any other particle-stabilized emulsions by choosing appropriate chemical reagent for dissolution.