Study of alkyl chain length dependent characteristics of imidazolium based ionic liquids [C_nMIM]⁺[TFSA]^? by Brillouin and dielectric loss spectroscopy

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• 作者：Hyun-Joung Kwon ; Jeong-Ah Seo ; Takashi Iwahashi ; Yukio Ouchi ; Doseok Kim ; Hyung Kook Kim ; Yoon-Hwae Hwang
• 关键词：Ionic liquid ; Imidazolium ; Alkyl chain length ; Domain formation
• 刊名：Current Applied Physics
• 出版年：2013
• 出版时间：January, 2013
• 年：2013
• 卷：13
• 期：1
• 页码：271-279
• 全文大小：2126 K

文摘

This study examined the acoustic phonon mode of ionic liquids consisting of 1-alkyl-3-methyl-imidazolium family (C_nMIM) cations with n values ranging from 2 to 10 and bis(trifluoromethylsulfonyl)amide (TFSA) anion in the temperature range from 300?K to 100?K. [C_nMIM]⁺[TFSA]^? showed depolarized (VH) components of Brillouin peaks at temperatures below the glass transition temperature when n is larger than 4. On the other hand, in the case of ionic liquids with different anions, such as [C₄MIM]⁺[BF₄]^?, [C₄MIM]⁺[PF₆]^? and [C₈MIM]⁺[BF₄]^?, the VH component of Brillouin peaks was not observed in the temperature range investigated. The dielectric loss spectra showed that the temperature dependence of alkyl chain domain relaxation of all ionic liquids followed the Arrhenius law and showed an increase in activation energy at the temperature where the VH component of Brillouin peak appeared. These results suggest that the observed depolarized component of Brillouin peak might originate from uniquely induced polarization in the 2nd domain composed of head groups of cations and anions.