Designed CO₂‐Philes Stabilize Water‐in‐Carbon Dioxide Microemulsions

Carbon dioxide/water, water/carbon dioxide emulsions and double emulsions stabilized with a nonionic biocompatible surfactant

“…Microemulsions are optically transparent, thermodynamically stable, isotropic mixtures of water, CO 2 , and surfactant, and typically consist of disperse phase droplets from 2 to 50 nm in diameter [1,2]. In contrast to microemulsions, (macro) [3][4][5][6][7][8] emulsions contain relatively large droplets (>0.1 lm) that are opaque and, although no longer thermodynamically stable, may be kinetically stable for long periods. Furthermore, emulsions may be formed with higher interfacial tensions between water and oil (or CO 2 ) than in the case of microemulsions and, thus, with lower values of surfactant adsorption at the interface.…”

“…Harrison et al [12] demonstrated that a dichain hybrid surfactant could microemulsify up to its own weight of water. Eastoe et al [7] reported the phase behavior data of the W/C microemulsion formed by fluorinated analogues of AOT and the size of the water droplet radius was measured by using small-angle neutron scattering (SANS). However, until now, the formation of water-in-CO 2 (W/C) microemulsions has been mostly demonstrated for fluoroether or hybrid fluorocarbon-hydrocarbon surfactants [7,[13][14][15][16][17].…”

“…Eastoe et al [7] reported the phase behavior data of the W/C microemulsion formed by fluorinated analogues of AOT and the size of the water droplet radius was measured by using small-angle neutron scattering (SANS). However, until now, the formation of water-in-CO 2 (W/C) microemulsions has been mostly demonstrated for fluoroether or hybrid fluorocarbon-hydrocarbon surfactants [7,[13][14][15][16][17]. In contrast, W/C macroemulsions can be formed by surfactants with hydrocarbon tails given the much lower interfacial area and less stringent requirements for the lowering of the interfacial tension; however, most of these surfactants have not been biocompatible [9].…”

Green chemistry: the emergence of a transformative framework

“…Surfactants for water-in-CO 2 microemulsions have made it possible to dissolve ionic compounds, a wider range of catalysts, and even biomolecules in CO 2 (76). Early research was based on perfluorinated and silicone compounds (77,78), but toxicity concerns led to development of hydrocarbon-based surfactants (79,80), some based on renewable resources (81). Recently, it was shown that ionic liquids can form reverse micelles in supercritical CO 2 , providing another strategy for dissolving highly polar chemicals in CO 2 (82).…”

Phase equilibrium for surfactant Ls-54 in liquid CO2 with water and solubility estimation using the Peng–Robinson equation of state

“…Therefore, efforts have been directed toward hydrocarbon surfactants [21-23], hybrid fluorocarbon-hydrocarbon surfactants [24-26], and O-surfactants by incorporating oxygen into the surfactant tails [27]. Different techniques have been used to characterize the water-in-CO 2 microemulsions, including nuclear magnetic resonance (NMR) [28-29], small angle x-ray scattering (SAXS) [30], and UV–vis spectrophotometry[30, 31].…”