Development of recyclable pH-responsive magnetic nanospheres via RAFT polymerization and their application in Pickering emulsions

A controllable and efficient method for the preparation of dual-stimulus-responsive magnetic nanospheres (IO/P) as particle emulsifiers via reversible surface addition and fragmentation chain transfer (RAFT) polymerization was described. FTIR, TGA, TEM and VSM were used to prove that the grafting reaction proceeded successfully. The interfacial properties of the magnetic nanospheres at pH from 2 to 12 were characterized by interfacial tension meter. The IO/P Pickering emulsion had dual-responsiveness of pH and magnetic, which was stable at pH 8–10, and could be rapidly broken by changing pH value or under the action of an external magnetic field. The emulsion could undergo at least 5 emulsification-demulsification cycles, which were triggered by changing pH value. The stabilization/destabilization of IO/P Pickering emulsions was triggered by the synergistic effect of applied magnetic field, surface wettability, and zeta potential, which led to the adsorption/exfoliation of IO/P on the water-oil interface. In addition, the effects of polymer segment length, particle concentration, water-oil ratio, and oil phase polarity on emulsion stability were investigated in detail. pH and magnetic stimuli-responsive Pickering emulsifier provided opportunities for oily wastewater treatment, water-oil separation, and design of crude oil delivery systems.