Influence of surfactant amphiphilicity on the phase behavior of IL-based microemulsions

Abstract

The authors report on the phase behavior of 1-Et-3-Me-imidazolium-ethylsulfate ([emim][etSO4])/limonene/polyethylene glycol tert-octylphenyl ether (Triton X-114 or TX-114) microemulsions as a function of ionic liq. (IL) content and temp. Phase diagrams, cond. measurements, and small angle x-ray scattering (SAXS) expts. will be presented. A hydrophilic IL, instead of H2O is used with the goal to enlarge the temp. range on which stable microemulsions can be formed. Indeed, the system shows remarkably large temp. stability, in particular down to -35°. The authors will emphasize on a comparison with a recently published work about microemulsions composed of [emim][etSO4], limonene, and Triton X-100 that to some extent are stable at temps. well below the f.p. of H2O. The key parameter responsible for the difference in phase behavior, microstructure, and temp. stability is the av. repeating no. of ethylene oxide units in the surfactant head group, which is smaller for Triton X-114 compared to Triton X-100. Among the fundamental interest, how the amphiphilicity of the surfactant influences the phase diagram and phase behavior of IL-based microemulsions, the exchange of Triton X-100 by Triton X-114 results in one main advantage: along the exptl. path the temp. where phase segregation occurs is significantly lowered leading to single phase microemulsions that exist at temps. beneath 0°.