Intermolecular vibrations and fast relaxations in supercooled ionic liquids.
Intermolecular vibrations and fast relaxations in supercooled ionic liquids.
复制标题
过冷离子液体中的分子间振动和快速弛豫。
DOI：
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发表时间：
2011
影响因子：
4.4
通讯作者：
M. Ribeiro
中科院分区：
文献类型：
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作者：
M. Ribeiro
用低频拉曼光谱(4<；ω<；100 cm(-1))研究了离子液体在过冷液体范围内的短时动力学。报道了具有相同阴离子、双(三氟甲基磺酰亚胺)和不同阳离子的离子液体的拉曼光谱：1-丁基-3-甲基咪唑、1-己基-3-甲基咪唑、1-丁基-1-甲基哌啶、三甲基丁基铵和三丁基甲基铵。结果表明，低频拉曼光谱与用于研究离子液体分子间振动的光学克尔效应(OKE)光谱具有相似的结果。通过对含有芳香族和非芳香族阳离子的离子液体的比较，确定了通常归因于咪唑环振动的拉曼光谱的特征。含有非芳香族阳离子的离子液体的快弛豫强度(准弹性散射)和分子间振动贡献(玻色子峰)明显低于咪唑离子液体。根据玻色子峰值的频率和声速的实验数据，估算了玻色子峰值振动的关联长度。与离子液体的中子和X射线散射测量中观察到的第一个尖锐衍射峰的位置相反，与咪唑阳离子中的烷基链长不同，与玻色子峰(∼19？)有关的相关长度并不改变。将QES强度在过冷液体范围内的变化率与最近报道的离子液体的超额熵、自由体积和均方位移数据进行了比较。离子液体中QES强度的温度依赖性说明了已提出的玻璃形成液体的短时间动力学和长时间结构弛豫之间的关系。
Short-time dynamics of ionic liquids has been investigated by low-frequency Raman spectroscopy (4 < ω < 100 cm(-1)) within the supercooled liquid range. Raman spectra are reported for ionic liquids with the same anion, bis(trifluoromethylsulfonyl)imide, and different cations: 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-butyl-1-methylpiperidinium, trimethylbutylammonium, and tributylmethylammonium. It is shown that low-frequency Raman spectroscopy provides similar results as optical Kerr effect (OKE) spectroscopy, which has been used to study intermolecular vibrations in ionic liquids. The comparison of ionic liquids containing aromatic and non-aromatic cations identifies the characteristic feature in Raman spectra usually assigned to librational motion of the imidazolium ring. The strength of the fast relaxations (quasi-elastic scattering, QES) and the intermolecular vibrational contribution (boson peak) of ionic liquids with non-aromatic cations are significantly lower than imidazolium ionic liquids. A correlation length assigned to the boson peak vibrations was estimated from the frequency of the maximum of the boson peak and experimental data of sound velocity. The correlation length related to the boson peak (∼19 Å) does not change with the length of the alkyl chain in imidazolium cations, in contrast to the position of the first-sharp diffraction peak observed in neutron and X-ray scattering measurements of ionic liquids. The rate of change of the QES intensity in the supercooled liquid range is compared with data of excess entropy, free volume, and mean-squared displacement recently reported for ionic liquids. The temperature dependence of the QES intensity in ionic liquids illustrates relationships between short-time dynamics and long-time structural relaxation that have been proposed for glass-forming liquids.
影响因子：
15
作者：
Turton, David A.;Hunger, Johannes;Wynne, Klaas
通讯作者：
Wynne, Klaas