Polarity of the interface in ionic liquid in oil microemulsions

Ionic liquid based microemulsions were characterized by absorption solvatochromic shifts, 1H NMR and kinetic measurements in order to investigate the properties of the ionic liquid within the restricted geometry provided by microemulsions and the interactions of the ionic liquid with the interface. Experimental results show a significant difference between the interfaces of normal water and the new ionic liquid microemulsions. Absorption solvatochromic shift experiments and kinetic studies on the aminolysis of 4-nitrophenyl laurate by n  -decylamine show that the polarity at the interface of the ionic liquid in oil microemulsions (IL/O) is higher than at the interface of water in oil microemulsions (W/O) despite the fact that the polarity of [bmim][BF4-] is lower than the polarity of water. 1H NMR experiments showed that an increase in the ionic liquid content of the microemulsion led to an increase in the interaction between [bmim][BF4-] and TX-100. The reason for the higher polarity of the microemulsions with the ionic liquid can be explained in terms of the incorporation of higher levels of the ionic liquid at the interface of the microemulsions, as compared to water in the traditional systems.

Water is a more polar solvent than [bmim][BF4] ionic liquid. However the interface of [bmim][BF4] ionic liquid in cyclohexane microemulsions is more polar than that corresponding to water in cyclohexane ones by using TX-100 as a surfactant. The reason for this discrepancy is the larger incorporation of ionic liquid than water to the interface of the microemulsion.Figure optionsDownload high-quality image (84 K)Download as PowerPoint slideHighlights
► [bmim][BF4-] ionic liquid is used instead of water in non-ionic surfactant based microemulsions.
► The interface of [bmim][BF4-] microemulsions is more polar than that corresponding to water in oil microemulsions.
► Ionic liquid penetration in the interface of the microemulsion is higher than that of water.
► Ionic liquid in oil microemulsions displaces the aminolysis of 4-nitrophenyl laurate to the dispersed phase.