Concentrated CO2-in-water emulsions with nonionic polymeric surfactants

Abstract Concentrated CO 2 -in-water (C/W) emulsions are reported for amphiphiles containing alkylene oxide-, siloxane-, and fluorocarbon-based tails as a function of temperature and salinity. Poly(ethylene oxide)– b –poly(butylene oxide) (EO 15 – b –BO 12 ) can emulsify up to 70% CO 2 with droplet sizes from 2 to 4 μm in diameter, as determined by video-enhanced microscopy. This emulsion is stable over 48 h against both flocculation and coalescence. In contrast, it is extremely difficult to form concentrated water-in-CO 2 (W/C) emulsions with surfactants containing alkylene oxide moieties due to limited solvation of such tails by CO 2 . In several cases, C/W emulsions are formed even when the surfactant prefers CO 2 . This violation of Bancroft's rule may be attributed in part to the low viscosity of the compressed CO 2 , which governs several mass and momentum transport mechanisms relevant to emulsion formation and stabilization. For the first time, W/C microemulsions are observed in a system with a nonionic amphiphile, namely F(CF 2 CF 2 ) 3–8 CH 2 CH 2 O(CH 2 CH 2 O) 10–15 H. For the same system, the emulsion morphology changes from C/W to W/C as the temperature increases. The electrical conductivity of C/W emulsions is predicted successfully as a function of the dispersed phase volume fraction of CO 2 with Maxwell's theory for inhomogeneous systems.