Phase behavior of Tween 80/SDBS mixed microemulsions and mechanistic insights into enhanced oil separation from aged oily sludge.

To address the demand for resource recovery of aged oily sludge (AOS), this study developed a middle-phase microemulsion (Winsor III microemulsion) using commercially available sodium dodecyl benzene sulfonate (SDBS) and Tween 80. A multiscale synergistic mechanism of "micro-triggering→interfacial regulation→macro-repair" was elucidated. By integrating one-dimensional (1D) and two-dimensional correlation spectroscopy (2D-COS, based on FTIR and Raman), we revealed the asynchronous molecular evolution during the oil-in-water (O/W)→Winsor III→water-in-oil (W/O) transition. Specifically, salinity-driven processes followed a "core-to-surface" sequence to induce conformational ordering, whereas n-butanol-driven processes followed a "surface-to-core" mode to regulate hydration states, revealing pronounced interfacial flexibility and curvature inversion. This molecular response promotes a more balanced interfacial organization with lower interfacial energy and marked wettability reversal (contact angle reduction > 40°). Molecular dynamics (MD) simulations, including hydrogen bond (H-bond) count statistics and interaction energy (Eint) analysis, revealed the distinct roles of the two surfactants at the atomic scale: SDBS maintains thermodynamic stability through interfacial electrostatic interactions, while Tween 80 acts as an interfacial anchor to facilitate the association and transfer of asphaltenes through specific hydrogen bond locking (1.28 Å). This enhances the incorporation and solubilization of petroleum components into the microemulsion core via a "local hydration enhancement" mechanism. Macroscopic evaluations showed that under mild conditions (45 °C), the residual oil rate (ROR) was reduced to < 0.3%. This study provides a rigorous multi-scale theoretical basis for interfacial regulation in AOS treatment.