3 research outputs found
Microstructure of ionic liquid (EAN)-rich and oil-rich microemulsions studied by SANS
In a previous study we investigated the phase behavior of microemulsions consisting of the ionic liquid ethylammonium nitrate (EAN), an n-alkane and a nonionic alkyl polyglycolether (CiEj). We found the same general trends as for the aqueous counterparts, i.e. a transition from an oil-in-EAN microemulsion via a bicontinuous microemulsion to an EAN-in-oil microemulsion with increasing temperature. However, unlike what happens in the corresponding aqueous systems, in EAN-in-oil microemulsions only a very small amount of EAN was detected by NMR-measurements. This is why we investigated the phase behavior and microstructure of EAN-rich n-dodecane-in-EAN microemulsions and oil-rich EAN-in-n-octane microemulsions. We found that the ionic liquid emulsification failure boundary has an extraordinarily small slope, which suggests that the amphiphilic film loses its ability to solubilize EAN with an increase in temperature by only a few degrees. The analysis of the small angle neutron scattering (SANS) curves unambiguously shows that this behavior is due to the fact that the EAN molecules form a substructure with a characteristic length scale of approximate to 8 angstrom inside the EAN-in-oil droplets. In more detail, the analysis of the SANS data with the GIFT method revealed a transition from spherical to cylindrical structures approaching the respective critical endpoint temperatures. By using the respective form factors and combining them with a Gaussian spatial intensity distribution to account for the EAN sub-structure we were able to describe the scattering curves nearly quantitatively
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 C<sub>12</sub>E<sub>3</sub> 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<sub>ab</sub> 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<sub>i</sub>E<sub>j</sub> 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