How Polar Are Ionic Liquids? Determination of the Static Dielectric Constant of an Imidazolium-based Ionic Liquid by Microwave Dielectric Spectroscopy

In a pilot study of the dielectric constant of room-temperature ionic liquids, we use dielectric spectroscopy in the megahertz/gigahertz regime to determine the complex dielectric function of five 1-alkyl-3-methylimidazolium salts, from which the static dielectric constant ε is obtained by zero-freq...

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Bibliographic Details
Published in:The journal of physical chemistry. B 2005-09, Vol.109 (36), p.17028-17030
Main Authors: Wakai, Chihiro, Oleinikova, Alla, Ott, Magnus, Weingärtner, Hermann
Format: Article
Language:English
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Summary:In a pilot study of the dielectric constant of room-temperature ionic liquids, we use dielectric spectroscopy in the megahertz/gigahertz regime to determine the complex dielectric function of five 1-alkyl-3-methylimidazolium salts, from which the static dielectric constant ε is obtained by zero-frequency extrapolation. The results classify the salts as moderately polar solvents. The observed ε-values at 298.15 K fall between 15.2 and 8.8, and ε decreases with increasing chain length of the alkyl residue of the cation. The anion sequence is trifluoromethylsulfonate > tetrafluoroborate ≈ tetrafluorophosphate. The results indicate markedly lower polarities than found by spectroscopy with polarity-sensitive solvatochromic dyes.
ISSN:1520-6106
1520-5207
DOI:10.1021/jp053946+