Browsing by Author "Liou, You-Chang"

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Effects of water and methanol on the molecular organization of 1-butyl-3-methylimidazolium tetrafluoroborate as functions of pressure and concentration
(2008-07-28)
Chang, Hai-Chou
;
Jiang, Jyh-Chiang
;
Liou, You-Chang
;
Hung, Chao-Hsin
;
Lai, Ting-Yun
The structural organization in mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)])/water or methanol was studied by infrared spectroscopy. No drastic change in the concentration dependence of the alkyl C-H band frequency was observed at high concentration of the ionic liquid. This behavior indicates a clustering of the ionic liquid in alkyl regions. Nevertheless, the presence of methanol significantly perturbs the ionic liquid-ionic liquid associations in the imidazolium region. On the basis of the responses to change in pressure and concentration, two different types of O-H species, i.e., free O-H and bonded O-H, were observed in the O-H stretching region. For [bmim][BF(4)]/water mixtures, the compression leads to loss of the free O-H band intensity. It is likely that free O-H is switched to bonded O-H as high pressures are applied. For [bmim][BF(4)]/methanol mixtures, the free O-H is still stable under high pressures. (C) 2008 American Institute of Physics.
Local Structures of Water in 1-Butyl-3-methylimidazolium Tetrafluoroborate Probed by High-Pressure Infrared Spectroscopy
(2008-10-01)
Chang, Hai-Chou
;
Jiang, Jyh-Chiang
;
Liou, You-Chang
;
Hung, Chao-Hsin
;
Lai, Ting-Yun
We have investigated the aggregation behaviors of water molecules in 1-butyl-3-methylimidazolium tetrafluoroborate/water mixtures using high-pressure methods. Under ambient pressure, the IR spectra indicate that two types of O-H species: free O-H and bonded O-H, existing in ionic liquid/water Mixtures. As samples were compressed, a continuous loss of the free O-H band intensity was observed. This observation may have arisen from changes in the local structures of water molecules, and the geometrical properties of the hydrogen-bond network are likely to be perturbed as the pressure is elevated. A complementary insight of the O-H spectral features is obtained by measuring the concentration-dependent variation in the mid-infrared spectra under high pressure. A sharp O-H stretching band was observed in a diluted mixture corresponding to the high order in an ice VII-Iike structure. Nevertheless, a very broad O-H feature was measured in a concentrated mixture, which may be attributed to the presence of more than one stable cluster.