Whereas numerous studies of stabilization of nanoparticles (NPs) in electrolytes have examined biological fluids, the interest has grown recently in media with much higher ionic strengths including seawater and brines relevant to environmental science and subsurface oil and gas reservoirs. Given that electrostatic repulsion is limited at extremely high ionic strengths due to charge screening, we have identified ligands that are well solvated in concentrated brine containing divalent cations and thus provide steric stabilization of silica nanoparticles. Specifically, the hydrodynamic diameter of silica nanoparticles with grafted low molecular weight ligands, a diol ether, [3-(2,3-dihydroxypropoxy)propyl]-trimethoxysilane, and a zwitterionic sulfobetaine, 3-([dimethyl(3-trimethoxysilyl)propyl]ammonio)propane-1-sulfonate, is shown with dynamic light scattering to remain essentially constant, indicating lack of aggregation, at room temperature and up to 80 °C for over 30 days. An extended DLVO model signifies that steric stabilization is strongly dominant against van der Waals attraction for ∼10 nm particles given that these ligands are well solvated even in highly concentrated brine. In contrast, polyethylene glycol oligomers do not provide steric stabilization at elevated temperatures, even at conditions where the ligands are soluble, indicating complicating factors including bridging of the ether oxygens by divalent cations.
Ultralow water content carbon dioxide-in-water (C/W) foams with gas phase volume fractions (ϕ) above 0.95 (that is <0.05 water) tend to be inherently unstable given that the large capillary pressures that cause the lamellar films to thin. Herein, we demonstrate that these C/W foams may be stabilized with viscoelastic aqueous phases formed with a single zwitterionic surfactant at a concentration of only 1% (w/v) in DI water and over a wide range of salinity. Moreover, they are stable with a foam quality ϕ up to 0.98 even for temperatures up to 120°C. The properties of aqueous viscoelastic solutions and foams containing these solutions are examined for a series of zwitterionic amidopropylcarbobetaines, R-ONHCHN(CH)CHCO, where R is varied from C (coco) to C (oleyl) to C (erucyl). For the surfactants with long C and C tails, the relaxation times from complex rheology indicate the presence of viscoelastic wormlike micelles over a wide range in salinity and pH, given the high surfactant packing fraction. The apparent viscosities of these ultralow water content foams reached more than 120cP with stabilities more than 30-fold over those for foams formed with the non-viscoelastic C surfactant. At 90°C, the foam morphology was composed of ∼35μm diameter bubbles with a polyhedral texture. The apparent foam viscosity typically increased with ϕ and then dropped at ϕ values higher than 0.95-0.98. The Ostwald ripening rate was slower for foams with viscoelastic versus non-viscoelastic lamellae as shown by optical microscopy, as a consequence of slower lamellar drainage rates. The ability to achieve high stabilities for ultralow water content C/W foams over a wide temperature range is of interest in various technologies including polymer and materials science, CO enhanced oil recovery, CO sequestration (by greater control of the CO flow patterns), and possibly even hydraulic fracturing with minimal use of water to reduce the requirements for wastewater disposal.
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