Miscibility and Distribution of Counterions of Imidazolium Ionic Liquid Mixtures at the Air/Water Surface

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• 作者：Kei Shimamoto ; Asuka Onohara ; Hiroki Takumi ; Iwao Watanabe ; Hajime Tanida ; Hiroki Matsubara ; Takanori Takiue ; Makoto Aratono
• 刊名：Langmuir
• 出版年：2009
• 出版时间：September 1, 2009
• 年：2009
• 卷：25
• 期：17
• 页码：9954-9959
• 全文大小：844K
• 年卷期：v.25,no.17(September 1, 2009)
• ISSN：1520-5827

文摘

The miscibility and distribution of Br⁻ and BF₄⁻ ions of imidazolium ionic liquid mixtures, 1-hexyl-3-methylimidazolium bromide (HMIMBr) + 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF₄), at the air/water surface were investigated by surface tensiometry and the total-reflection XAFS (TRXAFS) method. Tensiometry showed that the surface density of BF₄⁻ was much larger than that of Br⁻, the adsorbed films of the HMIMBr−HMIMBF₄ mixture were greatly enriched in BF₄⁻ at all surface tensions, and the excess Gibbs energy of adsorption was positive. However, TRXAFS revealed that the Br ions were all in the free-Br state solvated by six water molecules in the mixed adsorbed film. Entropy-originated nonideal mixing, where a kind of segregation of the counterion distribution takes place in the interfacial region, was suggested in the mixture.