Dual-Tail Trisiloxane Surfactants Stabilize Supercritical CO2 Nanoemulsions for Geological Carbon Sequestration

Nanoemulsions offer an approach that balances safety and efficiency in carbon sequestration. The addition of surfactants extends the lifetime of nanoemulsions to ensure stable efficacy. However, previous research on CO2 under atmospheric conditions cannot be applied to practical carbon sequestration due to the special properties of supercritical CO2. Furthermore, the complex and variable experimental environment hinders the summarization of patterns of surfactant interfacial behavior. Herein, we investigate the influencing factors of surfactant interfacial behavior at the molecular scale by combining the charge distribution characteristics of surfactants with the binding state of surrounding molecules. Our results show that T-PA5 exhibits the strongest polymerization inhibition effect, with the longest aggregation time of 156.72 ns, which is 109.98% higher than PA5. The binding state of the PA5 series surfactants (PA5s) undergoes a "parallel-quasi-parallel-cross" transition. This resistance to thermal fluctuations is attributed to the stable cross-bonding structure of T-PA5. The degree of self-folding at the sCO2-H2O interface varies drastically regarding Pro8 series surfactants (Pro8s). The unique self-folding configuration of TQ-Pro8 maintains optimal resistance to pressure fluctuations.