Electrostatic-induced jammed films lock displacement fronts in porous media

Surfactants are commonly used to enhance the fluid displacement in porous media for CO₂ sequestration, oil recovery, and soil remediation. However, unstable displacement patterns caused by viscous-capillary competition often lead to a small displacement efficiency, and the problematic emulsions also hinders the separation and sustainability. To address these limitations, we developed cationic carbon quantum dots (CQDs) via one-pot synthesis, enabling interfacial self-assembly with oil-phase molecules-specifically naphthenic acids (NAs)-to form a robust film. This film demonstrates two key characteristics: (i) strong CQDs-NAs binding energy (-150 kJ/mol), facilitating rapid adsorption-rearrangement and the formation of Turing-structured jammed assemblies; (ii) high mechanical strength, enabling resistance to structural rupture during mechanical penetration (puncture force: ∼0.32 mN). As a result, displacement fronts could be stabilized very well by suppressing viscous fingering at high capillary numbers (Ca) and the displacement efficiency in high-viscosity-ratio systems could be largely improved by mitigating oil-phase drag resistance, particularly in intermediate/weakly oil-wet conditions. Furthermore, this study introduces a CO₂/N₂-responsive design strategy for the CQDs, enabling reversible recycling in alignment with green chemistry principles and cost-efficient processes.