pH- and Salt-Responsive Pickering Polymer Emulsion for Controllable Release of Drag Reducers

To address the limitation of a single stimulus source in traditional switching emulsion drag reducers, increasing the variety of responsive groups to emulsifiers is one of the effective measures to broaden the release window of switchable emulsions and enhance the dissolution efficiency of the drag reducer. By leveraging the strong designability and interfacial stability of nanoparticles, multiresponsive switchable emulsion drag reducers were constructed, which effectively simplify the complexity of controlling the release of drag reducers. Herein, based on the concept that the pH sensitivity of the imine bond and the complexation of N with lone electron pairs to metal ions, we have developed a novel strategy for the synthesis of pH-responsive metal-organic frameworks (MOFs) with high stability and recyclability. A nanoparticle (SiO₂-NH₂@DF-DAP) with pH- and salt responsiveness was constructed to stabilize the switching Pickering emulsion drag reducer. The response behavior of switching Pickering emulsions was confirmed by the conductivity and fluorescence methods. The most stable Pickering emulsion optimized by centrifugation was used as a template for the preparation of a switching Pickering emulsion drag reducer. The switching Pickering emulsion drag reducer exhibited remarkable storage stability even after 45 days because the nanoparticles could stably adsorb on the oil-water interface to form an interfacial film with a rigid multilayer structure. Importantly, the switching Pickering emulsion drag reducer was completely released in only 20 s under the dual response of pH (4) and salt (the concentration of MgCl₂ was 70 mM). Besides, the drag reduction rate of the switching Pickering emulsion drag reducer was 65% at a concentration of 0.05 wt %. The successful construction of a switching Pickering emulsion drag reducer provides new strategies and insights for the efficient and rapid release of drag reducers.