Microemulsions with the Ionic Liquid Ethylammonium Nitrate: Phase Behavior, Composition, and Microstructure

In this study, we investigate properties of microemulsions which consist of the ionic liquid (IL) ethylammonium nitrate (EAN), the nonionic surfactant C₁₂E₃ and an <i>n</i>-alkane, namely <i>n</i>-dodecane or <i>n-</i>octane. The compositions of the coexisting phases are calculated from the densities and volumes of the respective phases. Since the interfacial tension between the water-rich and the oil-rich phase in traditional microemulsions (containing water and oil) relates to the microstructure, spinning drop tensiometry is used to measure the interfacial tension σ_ab and to estimate the domain sizes. Finally, measuring the self-diffusion coefficients of all components via the Fourier Transform Pulsed Gradient Spin Echo (FTPGSE) NMR technique allowed distinguishing between continuous and discrete structures. Our results indicate that the general principles underlying water–<i>n</i>-alkane–C_iE_j microemulsions can indeed be transferred to oil-in-EAN droplet and the respective bicontinuous microemulsions, while differences are observed for EAN-in-oil droplet microemulsions