Inelastic neutron scattering study on boson peaks of imidazolium-based ionic liquids

Maiko Kofu; Yasuhiro Inamura; Yosuke Moriya; Andrey Podlesnyak; Georg Ehlers; Osamu Yamamuro

doi:10.1016/j.molliq.2015.07.021

Inelastic neutron scattering study on boson peaks of imidazolium-based ionic liquids

Maiko Kofu, Yasuhiro Inamura, Yosuke Moriya, Andrey Podlesnyak, Georg Ehlers, Osamu Yamamuro

Research output: Contribution to journal › Article › peer-review

9 Scopus citations

Abstract

Low energy excitations of 1-alkyl-3-methylimidazolium ionic liquids (ILs) have been investigated by means of neutron spectroscopy. In the spectra of inelastic scattering, a broad excitation peak referred to as a "boson peak" appeared at 1-3 meV in all of the ILs measured. The intensity of the boson peak was enhanced at the Q positions corresponding to the diffraction peaks, reflecting the in-phase vibrational nature of the boson peak. Furthermore the boson peak energy (E_BP) was insensitive to the length of the alkyl-chain but changed depending on the radius of the anion. From the correlation among E_BP, the anion radius, and the glass transition temperature T_g, we conclude that both E_BP and T_g in ILs are predominantly governed by the inter-ionic Coulomb interaction which is less influenced by the alkyl-chain length. We also found that the E_BP is proportional to the inverse square root of the molecular weight as observed in molecular glasses.

Original language	English
Pages (from-to)	164-168
Number of pages	5
Journal	Journal of Molecular Liquids
Volume	210
DOIs	https://doi.org/10.1016/j.molliq.2015.07.021
State	Published - Oct 1 2015

Funding

We thank Prof. M. Nakakoshi, Dr. T. Ueki, and Prof. M. Watanabe in Yokohama National University for the synthesis of the samples. We are deeply grateful to the Oak Ridge National Laboratory for giving us the opportunity to carry out our experiments when the Japan Proton Accelerator Research Complex (J-PARC) was closed due to the earthquake in 2011. Research at ORNL's Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. This work is financially supported by the US–Japan Cooperative Program on Neutron Scattering .

Keywords

Boson peak
Glass
Inelastic neutron scattering
Ionic liquid

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10.1016/j.molliq.2015.07.021

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title = "Inelastic neutron scattering study on boson peaks of imidazolium-based ionic liquids",

abstract = "Low energy excitations of 1-alkyl-3-methylimidazolium ionic liquids (ILs) have been investigated by means of neutron spectroscopy. In the spectra of inelastic scattering, a broad excitation peak referred to as a {"}boson peak{"} appeared at 1-3 meV in all of the ILs measured. The intensity of the boson peak was enhanced at the Q positions corresponding to the diffraction peaks, reflecting the in-phase vibrational nature of the boson peak. Furthermore the boson peak energy (EBP) was insensitive to the length of the alkyl-chain but changed depending on the radius of the anion. From the correlation among EBP, the anion radius, and the glass transition temperature Tg, we conclude that both EBP and Tg in ILs are predominantly governed by the inter-ionic Coulomb interaction which is less influenced by the alkyl-chain length. We also found that the EBP is proportional to the inverse square root of the molecular weight as observed in molecular glasses.",

keywords = "Boson peak, Glass, Inelastic neutron scattering, Ionic liquid",

author = "Maiko Kofu and Yasuhiro Inamura and Yosuke Moriya and Andrey Podlesnyak and Georg Ehlers and Osamu Yamamuro",

year = "2015",

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doi = "10.1016/j.molliq.2015.07.021",

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T1 - Inelastic neutron scattering study on boson peaks of imidazolium-based ionic liquids

AU - Kofu, Maiko

AU - Inamura, Yasuhiro

AU - Moriya, Yosuke

AU - Podlesnyak, Andrey

AU - Ehlers, Georg

AU - Yamamuro, Osamu

PY - 2015/10/1

Y1 - 2015/10/1

N2 - Low energy excitations of 1-alkyl-3-methylimidazolium ionic liquids (ILs) have been investigated by means of neutron spectroscopy. In the spectra of inelastic scattering, a broad excitation peak referred to as a "boson peak" appeared at 1-3 meV in all of the ILs measured. The intensity of the boson peak was enhanced at the Q positions corresponding to the diffraction peaks, reflecting the in-phase vibrational nature of the boson peak. Furthermore the boson peak energy (EBP) was insensitive to the length of the alkyl-chain but changed depending on the radius of the anion. From the correlation among EBP, the anion radius, and the glass transition temperature Tg, we conclude that both EBP and Tg in ILs are predominantly governed by the inter-ionic Coulomb interaction which is less influenced by the alkyl-chain length. We also found that the EBP is proportional to the inverse square root of the molecular weight as observed in molecular glasses.

AB - Low energy excitations of 1-alkyl-3-methylimidazolium ionic liquids (ILs) have been investigated by means of neutron spectroscopy. In the spectra of inelastic scattering, a broad excitation peak referred to as a "boson peak" appeared at 1-3 meV in all of the ILs measured. The intensity of the boson peak was enhanced at the Q positions corresponding to the diffraction peaks, reflecting the in-phase vibrational nature of the boson peak. Furthermore the boson peak energy (EBP) was insensitive to the length of the alkyl-chain but changed depending on the radius of the anion. From the correlation among EBP, the anion radius, and the glass transition temperature Tg, we conclude that both EBP and Tg in ILs are predominantly governed by the inter-ionic Coulomb interaction which is less influenced by the alkyl-chain length. We also found that the EBP is proportional to the inverse square root of the molecular weight as observed in molecular glasses.

KW - Boson peak

KW - Glass

KW - Inelastic neutron scattering

KW - Ionic liquid

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DO - 10.1016/j.molliq.2015.07.021

M3 - Article

AN - SCOPUS:84940462436

SN - 0167-7322

VL - 210

SP - 164

EP - 168

JO - Journal of Molecular Liquids

JF - Journal of Molecular Liquids

ER -

Inelastic neutron scattering study on boson peaks of imidazolium-based ionic liquids

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Keywords

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