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Interfacial Properties of Fluorocarbon and Hydrocarbon Phosphate Surfactants at the Water−CO 2 Interface

2005; American Chemical Society; Volume: 44; Issue: 5 Linguagem: Inglês

10.1021/ie048999c

1520-5045

Jasper L. Dickson, P. Griffin Smith, Varun V. Dhanuka, Vibha Srinivasan, Matthew T. Stone, Peter J. Rossky, Jacqueline A. Behles, Jason S. Keiper, Bin Xu, Charles S. Johnson, Joseph M. DeSimone, Keith P. Johnston,

Methane Hydrates and Related Phenomena

With high-pressure pendant-drop tensiometry, the interfacial tension (γ) and surface excess (Γ∞) for a family of ionic surfactants with identical phosphate headgroups and varying fluorocarbon and hydrocarbon tail structures were examined at the water−CO2 interface. To compensate for the unusually weak CO2−surfactant tail interactions, we designed hydrocarbon tails with weak tail−tail interactions to achieve a more favorable hydrophilic−CO2-philic balance. Branching of hydrocarbon surfactant tails is shown to lead to more favorable adsorption at the interface, closer to that of fluorocarbon surfactants. γ for a double-tail hydrocarbon phosphate surfactant with a relatively high degree of tail branching was lowered from the water−CO2 binary interface value of about 20 mN/m at 25 °C and 340 bar to 3.7 mN/m. This reduction in γ is attributed to both a decrease in the free volume between tails at the interface and reduced tail−tail interactions. In addition to tail structure, the effects of surfactant counterion, salt concentration, temperature, and CO2 density on γ and Γ∞ were investigated. The hydrophilic−CO2-philic balances of these surfactants are mapped by investigating changes in interfacial tension with these formulation variables. Low-molecular-weight branched hydrocarbon ionic surfactants are shown to stabilize concentrated CO2-in-water emulsions for greater than 1 h.