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Journal of Solution Chemistry

, Volume 42, Issue 10, pp 1888–1901 | Cite as

Small-Angle Neutron Scattering Study on Aggregation of 1-Alkyl-3-methylimidazolium Based Ionic Liquids in Aqueous Solution

  • Takumi Kusano
  • Kenta Fujii
  • Masaaki Tabata
  • Mitsuhiro Shibayama
Article

Abstract

Aggregation structures of 1-alkyl-3-methylimidazolium based ionic liquids (ILs) in aqueous solution were investigated by small-angle neutron scattering (SANS) from the viewpoint of alkyl chain length, n, and anions (Cl, Br and trifluoromethanesulfonate, \( {\text{CF}}_{3} {\text{SO}}_{3}^{ - } \)). In [C4mIm+]-based IL systems, no noticeable SANS intensity was observed for all of the systems examined here, although aqueous [C4mIm+][\( {\text{BF}}_{4}^{ - } \)] solutions show a significant SANS profile originating from concentration fluctuations in the solution (Almasy et al. J Phys Chem B 112:2382–2387, 2008). This suggests that [C4mIm+][Cl], [C4mIm+][Br] and [C4mIm+][\( {\text{CF}}_{3} {\text{SO}}_{3}^{ - } \)] homogeneously mix with water, unlike the [C4mIm+][\( {\text{BF}}_{4}^{ - } \)] system, due to preferential hydration of the ions. In the case of the C n mIm cations with longer alkyl chain lengths (n = 8 and 12), SANS profiles were clearly observed in the aqueous solutions at IL concentrations of C IL > 230 and 20.0 mmol·dm−3, respectively. For aqueous [C8mIm+][Br] solutions, the asymptotic behavior of the scattering function varied largely from I(q) ~ q −2 to ~q −4 with increasing C IL, indicating that the solution changes from an inhomogeneous mixing state to a nano-scale micelle state. Aqueous [C12mIm+][Br] solutions show a typical SANS profile for micelle formation in solution. It was found from a model-fitting analysis that the structure of the [C12mIm+][Br] micelle is ellipsoidal, not spherical, in solutions over the C IL range examined here.

Keywords

Ionic liquid Aggregation Micelle formation Small-angle neutron scattering 

Notes

Acknowledgments

This work has been financially supported by Grant-in-Aids for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (No. 24750066 to KF, No. 22245018 to MS). The SANS experiments were performed with the approval of the Institute for Solid State Physics, The University of Tokyo (Proposal No. 8599 and 8847K), at the research reactor, JRR-3, Japan Atomic Energy Agency, Tokai, Japan.

Supplementary material

10953_2013_80_MOESM1_ESM.doc (230 kb)
Supplementary material 1 (DOC 230 kb)

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Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  1. 1.Institute for Solid State PhysicsThe University of TokyoKashiwaJapan
  2. 2.Department of Chemistry, Faculty of Science and EngineeringSaga UniversitySagaJapan

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