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Publication - Professor Julian Eastoe

    Water-in-CO2 Microemulsions Stabilized by Fluorinated Cation-Anion Surfactant Pairs

    Citation

    Sagisaka, M, Saito, T, Yoshizawa, A, Rogers, SE, Guittard, F, Hill, C, Eastoe, J & Blesic, M, 2019, ‘Water-in-CO2 Microemulsions Stabilized by Fluorinated Cation-Anion Surfactant Pairs’. Langmuir, vol 35., pp. 3445-3454

    Abstract

    High-water-content water-in-supercritical CO2 (W/CO2) microemulsions are considered to be green, universal solvents, having both polar and nonpolar domains. Unfortunately, these systems generally require environmentally unacceptable stabilizers like long and/or multifluorocarbon-tail surfactants. Here, a series of catanionic surfactants having more environmentally friendly fluorinated C4-C6 tails have been studied in terms of interfacial properties, aggregation behavior, and solubilizing power in water and/or CO2. Surface tensions and critical micelle concentrations of these catanionic surfactants are, respectively, lowered by ∼9 mN/m and 100 times than those of the constituent single fluorocarbon-tail surfactants. Disklike micelles in water were observed above the respective critical micelle concentrations, implying the catanionic surfactants have a high critical packing parameter, which should be suitable for the formation of reverse micelles. Based on visual observation of phase behavior and Fourier transform infrared spectroscopic and small-angle neutron scattering studies, one of the three catanionic surfactants tested was found to form transparent single-phase W/CO2 microemulsions with a water-to-surfactant molar ratio of up to ∼50. This is the first successful demonstration of the formation of W/CO2 microemulsions by synergistic ion-pairing of anionic and cationic single-tail surfactants. This indicates that catanionic surfactants offer a promising approach to generate high-water-content W/CO2 microemulsions.

    Full details in the University publications repository