title: Water-in-ionic liquid microemulsion formation in solvent mixture of aprotic and protic imidazolium-based ionic liquids.
abstract: We report that water-in-ionic liquid microemulsions (MEs) are stably formed in an organic solvent-free system, i.e., a mixture of aprotic (aIL) and protic (pIL) imidazolium-based ionic liquids (ILs) containing the anionic surfactant dioctyl sulfosuccinate sodium salt (AOT). Structural investigations using dynamic light, small-angle X-ray, and small-angle neutron scatterings were performed for MEs formed in mixtures of aprotic 1-octyl-3-methylimidazolium ([C8mIm(+)]) and protic 1-alkylimidazolium ([CnImH(+)], n = 4 or 8) IL with a common anion, bis(trifluoromethanesulfonyl)amide ([TFSA(-)]). It was found that the ME structure strongly depends on the mixing composition of the aIL/pIL in the medium. The ME size appreciably increases with increasing pIL content in both [C8mIm(+)][TFSA(-)]/[C8ImH(+)][TFSA(-)] and [C8mIm(+)][TFSA(-)]/[C4ImH(+)][TFSA(-)] mixtures. The size is larger for the n = 8 system than that for the n = 4 system. These results indicate that the shell part of MEs is composed of both AOT and pIL cation, and the ME size can be tuned by pIL content in the aIL/pIL mixtures.
authors.affiliation: Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Takumi
authors.initials: T
authors.lastname: Kusano
authors.forename: Kenta
authors.initials: K
authors.lastname: Fujii
authors.forename: Kei
authors.initials: K
authors.lastname: Hashimoto
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Shibayama