Formulation, stability, and synergistic characteristics of diesel-in-water Pickering emulsions stabilized by titanium carbide (Ti₃C₂T_x) MXene and Tween 40

Enhanced oil recovery (EOR) operations increasingly depend on emulsion-based formulations that exhibit long-term stability under reservoir conditions while minimizing surfactant dosage. In this context, hybrid systems combining nanoparticles and surfactants offer a promising route to achieving both interfacial stability and formulation efficiency. Among potential nanoparticle candidates, Ti₃C₂T_x MXene exhibits high surface area and interfacial activity. However, its application in diesel-in-water Pickering emulsions under EOR-relevant conditions has not been explored. Challenges such as high hydrophilicity and strong electrostatic repulsion have limited the use of unmodified MXene as a standalone stabilizer in colloidal systems. To address this limitation, diesel-in-water Pickering emulsions were formulated using DL-Ti₃C₂T_x MXene combined with Tween 40 (0.5 wt%) and antifoam (0.15 wt%), aiming to investigate their synergistic stabilization behavior across MXene concentrations ranging from 0.1 to 1.5 wt%. The MXene-only system exhibited complete and immediate phase separation, whereas the hybrid emulsions demonstrated markedly enhanced stability, with no phase separation observed at 0.1 and 0.5 wt% after 24 h. A concentration-dependent trend was evident. At lower MXene contents, interfacial adsorption improved, and droplet sizes remained small and uniform. At higher concentrations (≥ 1.0 wt%), aggregation increased, and demulsification became more pronounced. Interfacial tension decreased steadily with increasing MXene content, reaching 0.86 mN/m at 1.5 wt%, while zeta potential remained strongly negative (−47.7 mV at 0.5 wt%), indicating sufficient electrostatic repulsion. Rheological analysis revealed a transition to shear-thinning behavior at higher MXene contents, confirming the formation of internal network structures. Compared to other reported systems based on silica (SiO₂), zinc oxide (ZnO), or functionalized MXenes, the MXene-Tween 40 formulation achieved superior short- and long-term emulsion stability without requiring surface modification or external stimuli. To the best of our knowledge, this is the first study to report the successful stabilization of diesel-in-water Pickering emulsions using unmodified Ti₃C₂T_x MXene. These findings highlight the synergistic interaction between MXene and Tween 40 and present a robust, surfactant-lean formulation suitable for oilfield applications.