Lima Thamires A, Paschoal Vitor H, Faria Luiz F O, Ribeiro Mauro C C, Ferreira Fabio F, Costa Fanny N, Giles Carlos
Laboratório de Espectroscopia Molecular, Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, CP 26077, CEP 05513-970 São Paulo, SP, Brazil.
Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André, SP, Brazil.
J Chem Phys. 2016 Jun 14;144(22):224505. doi: 10.1063/1.4953415.
Phase transitions of the ionic liquids n-butyl-trimethylammonium bis(trifluoromethanesulfonyl)imide, [N1114][NTf2], and methyl-tributylammonium bis(trifluoromethanesulfonyl)imide, [N1444][NTf2], were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) measurements, and Raman spectroscopy. XRD and Raman spectra were obtained as a function of temperature at atmospheric pressure, and also under high pressure at room temperature using a diamond anvil cell (DAC). [N1444][NTf2] experiences glass transition at low temperature, whereas [N1114][NTf2] crystallizes or not depending on the cooling rate. Both the ionic liquids exhibit glass transition under high pressure. XRD and low-frequency Raman spectra provide a consistent physical picture of structural ordering-disordering accompanying the thermal events of crystallization, glass transition, cold crystallization, pre-melting, and melting. Raman spectra in the high-frequency range of some specific cation and anion normal modes reveal conformational changes of the molecular structures along phase transitions.
通过差示扫描量热法（DSC）、X射线衍射（XRD）测量和拉曼光谱研究了离子液体正丁基三甲基铵双（三氟甲磺酰）亚胺（[N1114][NTf2]）和甲基三丁基铵双（三氟甲磺酰）亚胺（[N1444][NTf2]）的相变。XRD和拉曼光谱是在大气压下作为温度的函数获得的，并且在室温下使用金刚石对顶砧池（DAC）在高压下也获得了XRD和拉曼光谱。[N1444][NTf2]在低温下经历玻璃化转变，而[N1114][NTf2]是否结晶取决于冷却速率。两种离子液体在高压下均表现出玻璃化转变。XRD和低频拉曼光谱为伴随结晶、玻璃化转变、冷结晶、预熔化和熔化等热事件的结构有序-无序提供了一致的物理图像。某些特定阳离子和阴离子正常模式的高频范围内的拉曼光谱揭示了分子结构沿相变的构象变化。
