Structure and dynamics of propylammonium nitrate-acetonitrile mixtures: An intricate multi-scale system probed with experimental and theoretical techniques
Structure and dynamics of propylammonium nitrate-acetonitrile mixtures: An intricate multi-scale system probed with experimental and theoretical techniques
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DOI：
10.1063/1.5021868
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发表时间：
2018-04-07
影响因子：
4.4
通讯作者：
Gontrani, Lorenzo
中科院分区：
文献类型：
--
作者：
Campetella, Marco;Mariani, Alessandro;Gontrani, Lorenzo
本文报道了一系列乙腈/硝酸丙铵混合物的结构和动力学性质随其组成的变化。这些体系在低q状态下的x射线衍射模式表现出不寻常的强度增加，并且它们的H-1-NMR扩散-有序NMR波谱（DOSY）光谱显示出不寻常的扩散系数。然而，这两种现象的量级在硝酸丙铵混合物中小于在相同助溶剂的硝酸乙铵混合物中观察到的，这表明阳离子烷基尾在这些观察中起重要作用。实验x射线散射数据与分子动力学模拟结果进行了比较，包括用于解释短程相互作用的从头算研究和用于描述长距离相互作用的经典模拟。更高水平的计算强调了离子液体中存在一个强氢键网络，即使在高乙腈浓度下也只有轻微的扰动。这些强相互作用导致NO3-振动的对称性破坏，在nu(3)反对称拉伸中分裂约88 cm（-1）。经典的力场模拟使用了更多的离子对，但不能完全描述最远范围的相互作用，尽管它们成功地解释了观察到的浓度趋势，模型的分析证实了这类样品的纳米非均匀性。AIP出版社出版。
In this article, we report the study of structural and dynamical properties for a series of acetonitrile/propylammonium nitrate mixtures as a function of their composition. These systems display an unusual increase in intensity in their X-ray diffraction patterns in the low-q regime, and their H-1-NMR diffusion-ordered NMR spectroscopy (DOSY) spectra display unusual diffusivities. However, the magnitude of both phenomena for mixtures of propylammonium nitrate is smaller than those observed for ethylammonium nitrate mixtures with the same cosolvent, suggesting that the cation alkyl tail plays an important role in these observations. The experimental X-ray scattering data are compared with the results of molecular dynamics simulations, including both ab initio studies used to interpret short-range interactions and classical simulations to describe longer range interactions. The higher level calculations highlight the presence of a strong hydrogen bond network within the ionic liquid, only slightly perturbed even at high acetonitrile concentration. These strong interactions lead to the symmetry breaking of the NO3- vibrations, with a splitting of about 88 cm(-1) in the nu(3) antisymmetric stretch. The classical force field simulations use a greater number of ion pairs, but are not capable of fully describing the longest range interactions, although they do successfully account for the observed concentration trend, and the analysis of the models confirms the nano-inhomogeneity of these kinds of samples. Published by AIP Publishing.