Grupo de Nanomateriais, Fotónica e Materia Branda, Departamentos de Física de Partículas e de Física Aplicada, Universidade de Santiago de Compostela, Campus Vida s/n, E-15782 Santiago de Compostela, Spain.
Dipartimento di Chimica, Sapienza Università di Roma, Piazzale Aldo Moro 5, I-00185 Roma, Italy.
J Chem Phys. 2017 Mar 28;146(12):124503. doi: 10.1063/1.4978943.
The structural and dynamical properties of bulk mixtures of long-chained primary and secondary alcohols (propanol, butanol, and 2-pentanol) with protic ionic liquids (ethylammonium and butylammonium nitrate) were studied by means of molecular dynamics simulations and small angle X-ray scattering (SAXS). Changes in the structure with the alcohol concentration and with the alkyl chain length of the alcohol moieties were found, showing variations in the radial distribution function and in the number of hydrogen bonds in the bulk liquids. Moreover, the structural behaviour of the studied mixtures is further clarified with the spatial distribution functions. The global picture in the local scale is in good agreement with the nanostructured solvation paradigm [T. Méndez-Morales et al. Phys. Chem. B 118, 761 (2014)], according to which alcohols are accommodated into the hydrogen bonds' network of the ionic liquid instead of forming clusters in the bulk. Indeed, our study reveals that the alcohol molecules are placed with their polar heads at the interfaces between polar and nonpolar nanodomains in the ionic liquid, with their alkyl chains inside the nonpolar organic nanodomains. The influence of alcohol chain length in the single-particle dynamics of the mixtures is also reported calculating the velocity autocorrelation function and vibrational densities of states of the different species in the ionic liquid-alcohol mixtures, and a weak caging effect for the ethylammonium cations independent of the chain size of the alcohols was found. However, the SAXS data collected for the studied mixtures show an excess of the scattering intensities which indicates that there are also some structural heterogeneities at the nanoscale.
通过分子动力学模拟和小角 X 射线散射（SAXS）研究了长链伯醇（丙醇、丁醇和 2-戊醇）与质子离子液体（乙基铵和丁基铵硝酸盐）的混合物的体相结构和动力学性质。发现随着醇浓度和醇部分的烷基链长度的变化，结构发生了变化，在体相液体中表现出径向分布函数和氢键数量的变化。此外，还通过空间分布函数进一步澄清了所研究混合物的结构行为。局部尺度上的整体图景与纳米结构化溶剂化范例[T. Méndez-Morales 等人，Phys. Chem. B 118, 761 (2014)]一致，根据该范例，醇被容纳在离子液体的氢键网络中，而不是在体相中形成簇。事实上，我们的研究表明，醇分子的极性头位于离子液体中极性和非极性纳米域之间的界面处，其烷基链位于非极性有机纳米域内。通过计算离子液体-醇混合物中不同物种的速度自相关函数和振动态密度，还报告了醇链长对混合物中单粒子动力学的影响，发现乙基铵阳离子存在弱的笼效应，与醇的链大小无关。然而，为所研究的混合物收集的 SAXS 数据显示出散射强度的过剩，这表明在纳米尺度上也存在一些结构异质性。
