title: Miscibility and distribution of counterions of imidazolium ionic liquid mixtures at the air/water surface.
abstract: The miscibility and distribution of Br(-) and BF(4)(-) ions of imidazolium ionic liquid mixtures, 1-hexyl-3-methylimidazolium bromide (HMIMBr) + 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF(4)), at the air/water surface were investigated by surface tensiometry and the total-reflection XAFS (TRXAFS) method. Tensiometry showed that the surface density of BF(4)(-) was much larger than that of Br(-), the adsorbed films of the HMIMBr-HMIMBF(4) 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.
authors.affiliation: Department of Chemistry, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Shimamoto
authors.forename: Asuka
authors.initials: A
authors.lastname: Onohara
authors.forename: Hiroki
authors.initials: H
authors.lastname: Takumi
authors.forename: Iwao
authors.initials: I
authors.lastname: Watanabe
authors.forename: Hajime
authors.initials: H
authors.lastname: Tanida
authors.forename: Hiroki
authors.initials: H
authors.lastname: Matsubara
authors.forename: Takanori
authors.initials: T
authors.lastname: Takiue
authors.forename: Makoto
authors.initials: M
authors.lastname: Aratono