Concentrated CO2-in-water emulsions with nonionic polymeric surfactants

Concentrated CO2-in-water (C/W) emulsions are reported for amphiphiles cont aining alkylene oxide-, siloxane-, and fluorocarbon-based tails as a functi on of temperature and salinity. Poly(ethylene oxide)-b-poly(butylene oxide) (EO15-b-BO12) can emulsify up to 70% CO2 with droplet sizes from 2 to 4 mu m in diameter, as determined by video-enhanced microscopy, This emulsion is stable over 48 h against both flocculation and coalescence. In contrast, i t is extremely difficult to form concentrated water-in-CO2 (W/C) emulsions with surfactants containing alkylene oxide moieties due to limited solvatio n of such tails by CO2. In several cases, C/W emulsions are formed even whe n the surfactant prefers CO2. This violation of Bancroft's rule may be attr ibuted in part to the low viscosity of the compressed CO2, which governs se veral mass and momentum transport mechanisms relevant to emulsion formation and stabilization. For the first time, WIC microemulsions are observed in a system with a nonionic amphiphile, namely F(CF2CF2)(3-8)CH2CH2O(CH2CH2O)( 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 emulsio ns is predicted successfully as a function of the dispersed phase volume fr action of CO2 with Maxwell's theory for inhomogeneous systems. (C) 2001 Aca demic Press.