Local structure at the air/liquid interface of room-temperature ionic liquids probed by infrared-visible sum frequency generation vibrational spectroscopy: 1-alkyl-3-methylimidazolium tetrafluoroborates.
The air/liquid interface of 1-alkyl-3-methylimidazolium tetrafluoroborates with the general formula [C(n)mim]BF(4) (n = 4-11) was studied using infrared-visible sum frequency generation (SFG) vibrational spectroscopy. The probability of the gauche defect per CH2-CH2 bond in the alkyl chain decreases as the number of carbon atoms in the alkyl chain increases. This observation suggests that the interaction between the alkyl chains is enhanced as the alkyl chain length becomes longer. The frequencies of the C-H stretching vibrational modes observed in the SFG spectra are higher than those of the corresponding peak positions observed in the infrared spectra of the bulk liquids. This shift is consistent with a structure in which the alkyl chain protrudes from the bulk liquid into the air. A local structure, which originates from the intermolecular interaction between the ionic liquid molecules, is proposed to explain these observations.
Iimori
Toshifumi
T
Research Center for Materials Science, Nagoya University, Nagoya 464-8602, Japan.
Iwahashi
Takashi
T
Kanai
Kaname
K
Seki
Kazuhiko
K
Sung
Jaeho
J
Kim
Doseok
D
Hamaguchi
Hiro-o
HO
Ouchi
Yukio
Y
D000388:Air; D001881:Borates / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013055:Spectrophotometry, Infrared / Q000379:methods; D013696:Temperature; D014732:Vibration
D001881:Borates; D052578:Ionic Liquids