Construction of a pH-Switchable Surfactant with Multiple Response Sites for Rapid Release of Emulsion Drag Reducer

The switchable emulsion drag reducer can effectively avoid the contradiction between the stability of the emulsion and the release of the drag reducer. Notably, the traditional switchable emulsion drag reducer is mainly stabilized by surfactants with a single-tail chain and a single response site, which leads to poor storage stability and low release efficiency. Constructing surfactants with dual tails and multiple response sites offers a promising strategy to improve both stability and release efficiency of the drag reducer. Herein, a surfactant (OLA-BPB) with multiple response sites was synthesized by amidation and the Schiff base reaction. The surface activity of OLA-BPB was sensitively regulated by pH stimulation due to the existence of a tertiary amine group and imine bonds. The emulsion drag reducer prepared by inverse emulsion polymerization of the OLA-BPB-stabilized monomer emulsion exhibited favorable storage stability at 25 °C. The instability behavior of the emulsion drag reducer under pH stimulation was attributed to pH-induced changes in the surface activity of OLA-BPB. Thanks to this specialty, the pH-switchable emulsion drag reducer can be released within a broad pH value window (a range of 2 to 6) and can be completely released within 20 s at pH 3. The drag reduction rate of pH-switchable emulsion drag reducer reached 68.48% at a concentration of 0.05 wt %. The construction of the OLA-BPB offers an alternative option to enhancing the release efficiency of the drag reducer.