CO ₂ -responsive dynamic imine surfactant for enhanced oil recovery and on-demand demulsification of produced fluids

Emulsification flooding is a key mechanism for enhanced oil recovery. However, while strong emulsification significantly improves displacement efficiency, it concurrently poses substantial challenges to the subsequent oil–water separation of produced fluids. Therefore, developing smart surfactants that integrate robust emulsifying capacity with facile and efficient demulsification functionality is of considerable importance. In this study, a novel CO2-responsive surfactant (DFD-DA) featuring a dynamic imine bond was synthesized via a Schiff base reaction between disodium 4-formylbenzene-1,3-disulfonate (DFD) and dodecylamine. Its interfacial activity, emulsification performance, and oil displacement efficiency were systematically evaluated. The CO2-responsive demulsification behavior was examined, and the underlying emulsification mechanism was further elucidated through molecular dynamics simulations, complemented by experimental evidence. Results demonstrate that blending DFD-DA with lauroamidopropyl hydroxysulfobetaine (LHSB) at a 1:2 molar ratio significantly reduces interfacial tension to an order of 10−1 mN/m. This blended system exhibits exceptional emulsification performance, achieving an emulsified oil rate (E0) of 91.67% ± 1.05% and an emulsification index (EI) of 1.48 ± 0.03, along with remarkable CO2 responsiveness. Microscopic oil displacement experiments confirmed that the system effectively mobilizes crude oil and enhances the recovery of residual oil. Molecular simulation results provided supplementary insights into the emulsification process and the stabilization mechanism at the molecular level. This work presents a promising CO2-responsive surfactant system for both enhanced oil recovery and controllable demulsification in high water-cut oilfields.