Engineered Nanoparticles with Improved Foamability for Solely Stabilizing Pickering CO₂ Foam

CO₂ foam injection is a promising strategy for improving the safety and efficiency of CO₂ sequestration in saline aquifers. However, Classical foams stabilized by surfactants often suffer from poor stability under harsh reservoir conditions, while Mixed foams stabilized by physical mixtures of surfactants and nanoparticles usually exhibit a narrow stability window because of competitive adsorption and interfacial instability at high surfactant loadings. To address these limitations, we synthesized surfactant-tailored nanoparticles to solely stabilize Pickering CO₂ foams. Foam stability was systematically evaluated through half-life tests, bubble-size evolution in planar and vertical directions, and time-resolved measurements of CO₂-water interfacial film thickness. Compared with Classical foam and Mixed foam, the Pickering foam exhibits higher foamability and superior stability over a broader range of conditions. Under ambient conditions, it showed about 20 times higher foamability and a 3-fold longer half-life than Classical foam, while also outperforming Mixed foam. Under harsh conditions, including elevated temperature, high salinity, and the presence of hydrocarbons, its stability remained three to five times higher than those of the reference systems. Microscopic observations showed that the Pickering foam exhibits smaller and more uniform bubbles, slower coarsening, and thicker interfacial films than both the Classical foam and the Mixed foam, indicating stronger resistance to drainage and coalescence. A thin-film drainage model coupling hydrodynamic flow with interfacial adsorption energetics captured the experimental stability trends and attributed the improved performance to reduced capillary pressure, increased effective film viscosity, and enhanced structural disjoining pressure. These results demonstrate that surfactant-tailored nanoparticles can independently stabilize CO₂ Pickering foams without relying on excess free surfactant, offering an effective strategy for designing robust foam stabilizers for subsurface CO₂ sequestration.