Interplay of Interfacial and Rheological Properties on Drainage Reduction in CO2 Foam Stabilised by Surfactant/Nanoparticle Mixtures in Brine

Although nanoparticles (NPs) are known to increase foam stability, foam stabilisation is not observed in all surfactant/NP combinations. The present study evaluates the stability of CO2 foams containing surfactant/NP mixtures with attractive or repulsive electrostatic interactions at the low pH imposed by CO2 in the presence of a high-salinity brine. Three ionic surfactants and two oxide NPs (SiO2 and Al2O3) were used in combinations of similar or opposite charges. Surface tension, viscosity, ζ-potential and hydrodynamic size experiments allowed the analysis of CO2 foam stability based on the impact of surfactant–NP interactions on bulk and interfacial properties. All oppositely charged systems improved the foam half-life; however, a higher NP concentration was required to observe a significant effect when more efficient surfactants were present. Both bulk viscosity and rigidity of the interfacial films drastically increased in these systems, reducing foam drainage. The mixture of SiO2 with a zwitterionic surfactant showed the greatest increase in CO2 foam stability owing to the synergy of these effects, mediated by attractive interactions. This study showed that the use of NPs should be tailored to the surfactant of choice to achieve an interplay of interfacial and rheological properties able to reduce foam drainage in applications involving CO2 foam in brine.