Water-in-Carbon Dioxide Emulsions:  Formation and Stability

Stable water-in-carbon dioxide (W/C) emulsions, for either liquid or supercritical CO2 containing up to 70 vol % water, are formed with various molecular weight perfluoropolyether ammonium carboxylate surfactants. Water droplet sizes ranging from 3 to 10 μm were determined by optical microscopy. Fro...

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Bibliographic Details
Published in:Langmuir 1999-09, Vol.15 (20), p.6781-6791
Main Authors: Lee, C. Ted, Psathas, Petros A, Johnston, Keith P, deGrazia, Janet, Randolph, Theodore W
Format: Article
Language:English
Subjects:
CARBON DIOXIDE
EMULSIONS
ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
MATERIAL SUBSTITUTION
ORGANIC SOLVENTS
PHASE STUDIES
SYNTHESIS
WATER
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Summary:Stable water-in-carbon dioxide (W/C) emulsions, for either liquid or supercritical CO2 containing up to 70 vol % water, are formed with various molecular weight perfluoropolyether ammonium carboxylate surfactants. Water droplet sizes ranging from 3 to 10 μm were determined by optical microscopy. From conductivity measurements, an inversion to C/W emulsions results from a decrease in CO2 density or salinity at constant pressure, a decrease in surfactant molecular weight, or an increase in temperature. Emulsions become more stable with a change in any of these formulation variables away from the balanced state, which increases interfacial tensions and interfacial tension gradients, enhancing Marangoni−Gibbs stabilization. This type of stability is enhanced with an increase in the molecular weight of the surfactant tails, which increases the thickness of the stabilizing films between droplets. W/C emulsions formed with the 7500 molecular weight surfactant were stable for several days.
ISSN:0743-7463
1520-5827
DOI:10.1021/la9903548