Miscibility and distribution of counterions of imidazolium ionic liquid mixtures at the air/water surface

Kei Shimamoto; Asuka Onohara; Hiroki Takumi; Iwao Watanabe; Hajime Tanida; Hiroki Matsubara; Takanori Takiue; Makoto Aratono

doi:10.1021/la901114e

Miscibility and distribution of counterions of imidazolium ionic liquid mixtures at the air/water surface

Kei Shimamoto, Asuka Onohara, Hiroki Takumi, Iwao Watanabe, Hajime Tanida, Hiroki Matsubara, Takanori Takiue, Makoto Aratono

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

14 Citations (Scopus)

Abstract

The miscibility and distribution of Br^- and BF₄ ^- ions of imidazolium ionic liquid mixtures, l-hexyl-3- methylimidazolium bromide (HMIMBr) + l-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 BF ₄^- 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.

Original language	English
Pages (from-to)	9954-9959
Number of pages	6
Journal	Langmuir
Volume	25
Issue number	17
DOIs	https://doi.org/10.1021/la901114e
Publication status	Published - Sep 1 2009

All Science Journal Classification (ASJC) codes

Materials Science(all)
Condensed Matter Physics
Surfaces and Interfaces
Spectroscopy
Electrochemistry

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@article{6dc02b8c809843e9af1f6e43f42c408f,

title = "Miscibility and distribution of counterions of imidazolium ionic liquid mixtures at the air/water surface",

abstract = "The miscibility and distribution of Br- and BF4 - ions of imidazolium ionic liquid mixtures, l-hexyl-3- methylimidazolium bromide (HMIMBr) + l-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 BF 4- 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.",

author = "Kei Shimamoto and Asuka Onohara and Hiroki Takumi and Iwao Watanabe and Hajime Tanida and Hiroki Matsubara and Takanori Takiue and Makoto Aratono",

year = "2009",

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doi = "10.1021/la901114e",

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volume = "25",

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journal = "Langmuir",

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T1 - Miscibility and distribution of counterions of imidazolium ionic liquid mixtures at the air/water surface

AU - Shimamoto, Kei

AU - Onohara, Asuka

AU - Takumi, Hiroki

AU - Watanabe, Iwao

AU - Tanida, Hajime

AU - Matsubara, Hiroki

AU - Takiue, Takanori

AU - Aratono, Makoto

PY - 2009/9/1

Y1 - 2009/9/1

N2 - The miscibility and distribution of Br- and BF4 - ions of imidazolium ionic liquid mixtures, l-hexyl-3- methylimidazolium bromide (HMIMBr) + l-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 BF 4- 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.

AB - The miscibility and distribution of Br- and BF4 - ions of imidazolium ionic liquid mixtures, l-hexyl-3- methylimidazolium bromide (HMIMBr) + l-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 BF 4- 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.

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