Experimental and molecular dynamics study of the effect of betaine surfactant structure on CO2 foam stability

The stability of foams is crucial for enhancing CO2 flooding efficiency and reservoir storage capacity, and the zwitterionic inner salt structure of betaine surfactants exerts a significant effect on the stability of CO2 foams. This study focuses on revealing the structure-activity relationship between betaine structure and CO2 foam performance. By combining experimental measurements with molecular dynamics simulations, the influence mechanism of the hydrophilic group and hydrophobic chain structure of betaine on the stability of CO2 foam was systematically investigated. Results show that the increase of the carbon chain and sulfonyl substitution of betaine significantly enhanced the stability of CO2 foam, and strengthened the foam lamella strength by improving the interfacial adsorption and increasing the viscosity of the interfacial film. Molecular dynamics simulations further revealed that sulfo-betaines retarded foam decay by locking H2O molecules through strong hydrogen bonds and enhancing CO2 molecular binding by long-chain alkyl groups. This study not only advances the knowledge of the relationship between betaine structure and foam performance, but also provides direction for the design of new surfactants.