Intensifying the Mild-pH Responsiveness of Polymer Emulsions via Dual-Site Surfactant

As the focus of oil and gas extraction shifts toward unconventional reservoirs, improving the stability and solubility of polyacrylamide (PAM) emulsion drag reducers is critical for enhancing reservoir fracturing efficiency. However, persistent pH fluctuations in field environments remain a major obstacle to the application of existing PAM systems, which rely solely on a single responsive site. In this study, a dual-site surfactant, DEAB/OLA, was synthesized using 4-diethylaminobenzaldehyde and oleylamine as raw materials. Using DEAB/OLA-stabilized monomer emulsion as a template, the switchable polymer emulsion was prepared via inverse emulsion polymerization. The resulting emulsion remained stable during storage at 25 °C for up to 50 days. Its pH-responsive release behavior originates from a structural transformation of the surfactant at the oil–water interface. At pH 5.0, the combined effect of imine bond cleavage and tertiary amine protonation disrupts the interfacial film, whereas at pH 9.0, deprotonation of the tertiary amine alone causes the surfactant to detach from the interface. Owing to this synergistic mechanism, the emulsion released the polymer within 20 s at both pH 5.0 and pH 9.0. In pure water and standard brine, a 0.05 wt % polymer solution achieved drag reduction rates of 71.6% and 60.5%, respectively. This dual-site strategy provides a general approach for designing switchable polymer emulsions with a broad pH response window under mild conditions.