Interfacial properties and foam performance of alpha olefin sulfonate and CO₂ switchable aminopropyl methyl siloxane surfactant mixtures

CO2‐in‐water (C/W) foams have attracted much attention given their eco‐friendliness in recent years. However, limited surfactants were able to effectively adsorb at the supercritical CO2–water (C–W) interface considering the weak solvent strength of CO2, especially at high temperatures. Herein, attempts have been made to design suitable CO2 foaming agents by evaluating the influence of proportions of anionic and cationic surfactants and the affinity between aminopropyl methyl siloxane (APSi) and CO2. Through systematical foamability and foam stability experiments, together with the measurements of C–W equilibrium and dynamic interfacial tensions, the adsorption and stabilization mechanisms of sodium alpha olefin sulfonate (AOS)‐APSi aqueous dispersions on the CO2 foam films are revealed. Excellent foam properties were observed at AOS/APSi mass ratio of 9:1, in which initial foam height (h0) and half‐life period (t1/2) first increased and then decreased with increasing pressure, whereas the interfacial tension decreased with increasing pressure. The results indicate that the interaction of anionic and cationic head‐groups contributes to accelerating the surfactant adsorption rate from bulk to the C–W interface, enhancing foamability and stabilizing foam. Besides, the AOS/APSi mass ratio of 8:2 shows a good affinity for CO2 at 15 MPa, of which h0 is 26% higher and t1/2 is 60% slower than AOS alone. Furthermore, the initial mean bubble area of both 9:1 and 8:2 AOS/APSi mixtures was around half that of AOS alone. This work broadens the design of novel surfactant methodologies including CO2 foam, providing a theoretical guidance for the application of CO2 on enhanced‐oil‐recovery technologies.