Alcohol as tuning parameter in an IL-containing microemulsion: The quaternary system EAN –n- octane–C 12 E 3 –1-octanol

Abstract

Abstract 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 (C i E j ) 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–C i E j 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–C 12 E 3 − 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.