Design and optimization of surfactants and surface-modified nanoparticles for mechanistic studies of foam stabilization and interfacial interactions
Surfactants and/or nanoparticles (NP) are shown to stabilize carbon dioxide CO₂-in-water (C/W) foams and nitrogen N₂-in-water (N/W) foams with strong interfacial adsorption and interactions. The first two studies demonstrate that viscous C/W foams may be generated with either a single zwitterionic surfactant or a single switchable diamine surfactant, over a wide temperature range up to 150 °C even at high salinities. The foams have apparent viscosities in the right range to have potential in CO₂ mobility control based on the experimental results in porous media. Moreover, both surfactants are shown to have high thermal stability with negligible chemical degradation after incubation at 135 °C for 30 days, which benefits long-term applications in high temperature reservoir conditions. To another topic, the binary grafting of ether diol and dimethylsilyl ligands on silica NPs are then shown to provide steric stabilization in bulk phase of concentrated brine and raise the NP hydrophobicity to promote interfacial adsorption, producing an interface with a relatively strong surface elastic dilational modulus E'. The NP-laden interface also demonstrates moderate ductility with a relatively slow change in surface pressure Π and E' over a wide range of surface area variation during compression and expansion. Moreover, the combination of an anionic surfactant with NPs grafted with the binary ligands, each of which is interfacial-active, produces a highly viscoelastic air-brine interface at high salinity that enabled highly stable N/W foams from ambient temperature up to 80 °C. The ability to tailor the interfacial properties with surfactants and NPs with independently tunable surfaces is of broad scientific interest and great potential for various applications.