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Chemical Potentials in Aqueous Solutions of Some Ionic Liquids with the 1-Ethyl-3-methylimidazolium Cation

TitleChemical Potentials in Aqueous Solutions of Some Ionic Liquids with the 1-Ethyl-3-methylimidazolium Cation
Publication TypeJournal Article
Year of Publication2008
AuthorsKato, H, Nishikawa, K, Murai, H, Morita, T, Koga, Y
JournalJournal of Physical Chemistry B
Volume112
Pagination13344-13348
Date PublishedOct
Type of ArticleArticle
ISBN Number1520-6106
Keywords1-BUTYL-3-METHYLIMIDAZOLIUM, ACETONITRILE, AGGREGATION BEHAVIOR, ENTHALPY-ENTROPY COMPENSATION, MIXING SCHEMES, MOLECULAR-ORGANIZATION, SYSTEMS, TETRAFLUOROBORATE, TETRAFLUOROBORATE PLUS WATER, THERMODYNAMIC APPROACH, VAPOR-PRESSURE MEASUREMENT
Abstract

We determined the vapor pressures of aqueous solutions of 1-ethyl-3-methylimidazolium ([C(2)mim])-based ionic liquids (IL) with counteranions, tetrafluoroborate (BF4-), trifluoromethanesulfonate (OTF-), and iodide (I-) Because in literature the evidence is accumulating and pointing to the fact that ionic liquid ions do not dissociate in aqueous media for the most of the concentration range, we analyzed the vapor pressure data on the basis of binary mixture, and the excess chemical potentials of each component were calculated. From these, the intermolecular interactions in terms of excess chemical potential and hence the concentration fluctuations were evaluated. Though any further discussion into the mixing schemes of the mixture awaits the excess partial molar enthalpy and hence the excess partial molar entropy data, the net interaction in terms of excess chemical potential indicates that the affinity of each IL is ranked in the descending order [C2mim]l > [C(2)mim]OTF > [C(2)mim]BF4. This is consistent with our earlier findings that [C(2)mim](+) is modestly amphiphilic with almost equal hydrophobicity and hydrophilicity, I- is a hydrophile, and OTF- is amphiphilic, and BF4- is believed to be strongly hydrophobic.

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