Miscibility and distribution of counterions of imidazolium ionic liquid mixtures at the air/water surface.
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.
Shimamoto
Kei
K
Department of Chemistry, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan.
Onohara
Asuka
A
Takumi
Hiroki
H
Watanabe
Iwao
I
Tanida
Hajime
H
Matsubara
Hiroki
H
Takiue
Takanori
T
Aratono
Makoto
M