Alcohol as tuning parameter in an IL-containing microemulsion: The quaternary system EAN–n-octane–C12E3–1-octanol

• Alcohol as tuning parameter for the curvature in an IL-containing microemulsion.
• General patterns of IL- and water-containing microemulsions: similarities and differences.
• Discussion of monomeric solubilities of both surfactant and alcohol.
• First values for the saddle-splay and the bending rigidity of an IL-containing microemulsion.

With an appropriate tuning parameter a microemulsion can be forced to undergo a phase inversion, i.e. to invert the curvature of the amphiphilic film. In microemulsions consisting of water, an n-alkane and a nonionic alkyl polyglycolether (CiEj) temperature is an appropriate parameter since the surfactant head groups dehydrate with increasing temperature. Recently we were able to show that this also holds true for ethylammonium nitrate (EAN)–n-alkane–CiEj systems. However, the temperature sensitivity is weaker which is why we decided to use a hydrophobic cosurfactant to induce a phase inversion in the EAN-containing microemulsion. We studied the quaternary system EAN–n-octane–C12E3 − 1-octanol as a function of the alcohol concentration at T = 15 °C and found the same trends as for the aqueous counterparts. (1) Studying the phase behavior as a function of the alcohol content (δ) and of the total surfactant concentration (γ), one finds that the phase boundaries resemble the shape of a fish. (2) Measuring the interfacial tension σ between the IL- and oil-rich phase, one observes a minimum in the center of the three-phase region. (3) NMR self-diffusion measurements reveal a transition from an oil-in-EAN microemulsion to a bicontinuous microemulsion and finally to an EAN-in-oil microemulsion.

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