p046

M. Aono,^A Y. Imai,^A Y. Ogata,A H. Abe,^A T. Goto,^B Y. Yoshimura,^B T. Takekiyo,^B H. Matsumoto^A and T. Arai^C
^ADepartment of Materials Science and Engineering, National Defense Academy,
Yokosuka, Kanagawa, 239-8686, Japan
^BDepartment of Applied Chemistry, National Defence Academy, Yokosuka,
Kanagawa, 239-8686, Japan
^CDepartment of Applied Physics, National Defence Academy, Yokosuka,
Kanagawa, 239-8686, Japan

Metallurgical and Materials Transactions 42A, pp. 37-40 (2011.01).

Abstract

The mixing states of room-temperature ionic liquid (RTIL) H₂O mixtures (x = 0.0 mol pct to 99.5 mol pct H₂O) were investigated using wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), and optical absorption in an ultraviolet and visible (UV-vis) region. The RTIL is N, N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate, [DEME][BF₄]. In a ‘‘prepeak’’ region of the WAXS, the scattered intensities increased at 85 mol pct to 95 mol pct. A medium-range order (MRO) in the liquid structure as observed in network-forming materials developed markedly. In the SAXS experiments, we can detect nanoscale fluctuations relating to polar and nonpolar regions. At 65 mol pct to 85 mol pct, the SAXS intensity increased unexpectedly. Furthermore, entirely different optical absorption spectra in the UV-vis region were observed as a macroscopic property from 90 mol pct to 95 mol pct. We suppose that these anomalies relate to the MRO of the liquid structure. All anomalies probably are induced by an intrinsic property in [DEME][BF₄]-H₂O mixtures.

	Fig. 1. WAXS intensity changes in [DEME][BF₄]-H₂O mixtures at room temperature. Above 80 mol pct H₂O, the maximum position of the normal principal peak in WAXS gradually shifts to one of pure water.
	Fig. 2. H₂O concentration dependence of intensity of the low-Q component in WAXS. Q positions are 2.1 nm.1 and 3.1 nm^-1, which are provided by the allowances in Figure 1.
	Fig. 3. SAXS intensities as a function of the H₂O concentration.
	Fig. 4. H₂O concentration dependence of correlation length x, which is obtained with the Ornstein-Zernike correlation function.
	Fig. 5. Optical absorption spectra as a function of water concentration. The inset shows the absorption spectrum of pure water.
	Fig. 6. Water concentration dependence of the optical absorption coefficient at 4.7 eV.

References

1. D.A. Allen, R.A. Howe, N.D. Wood, and W.S. Howells: J. Phys.: Condens. Matter, 1992, vol. 4, pp. 1407-18.
2. M. Salanne, C. Simon, P. Turq, and P.A. Madden: J. Phys.: Condens. Matter, 2008, vol. 20, pp. 2101-15.
3. W. Welton: Chem. Rev., 1999, vol. 99, pp. 2071-83.
4. W. Leitner: Pure Appl. Chem., 2004, vol. 76, pp. 635-44.
5. H. Katayanagi, K. Nishikawa, H. Shimozaki, K. Miki, P. Westh, and Y. Koga: J. Phys. Chem. B, 2004, vol. 108, pp. 19451-57.
6. K.R. Seddon, A. Stark, and M-J Torres: Pure Appl. Chem., 2000, vol. 72, pp. 2275-87.
7. M. Deetlefs, C. Hardacre, M. Nieuwenhuyzen, O. Sheppard, and A. K. Soper: J. Phys. Chem. B, 2005, vol. 109, pp. 1593-98.
8. A. Triolo, O. Russina, H-J. Bleif, and E.D. Cola: J. Phys. Chem. B, 2007, vol. 111, pp. 4641-44.
9. J. Bowers, C.P. Butts, P.J. Martin, M.C. Vergara-Guterrez, and R.K. Heenan: Langmuir, 2004, vol. 20, pp. 2191-98.
10. W. Jiang, Y. Wang, and G.A. Voth: J. Phys. Chem. B, 2007, vol. 111, pp. 4812-18.
11. T. Sato, G. Masuda, and K. Takagi: Electrochim. Acta, 2004, vol. 49, pp. 3603-11.
12. H. Abe, Y. Imai, T. Takekiyo, and Yukihiro Yoshimura: J. Phys. Chem. B, 2010, vol. 114, pp. 2834-39.
13. H.E. Stanley: Introduction to Phase Transition and Critical Phenomena, Oxford University Press, New York, NY, 1971.
14. D.R. Barker, M. Wilson, P.A. Madden, N.N. Medvedev, and A. Geiger: Phys. Rev. E, 2000, vol. 62, pp. 1427-30.
15. A. Paul, P.K. Mandal, and A. Samanta: Chem. Phys. Lett., 2005, vol. 402, pp. 375-79.
16. S. Mahanta, R.B. Singh, S. Kar, and N. Guchhait: Chem. Phys., 2008, vol. 354, pp. 118-29.

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