Temperature Dependence of Static Structure Factor Peak Intensities for a Pyrrolidinium-Based Ionic Liquid
Temperature Dependence of Static Structure Factor Peak Intensities for a Pyrrolidinium-Based Ionic Liquid
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吡咯烷鎓基离子液体静态结构因子峰强度的温度依赖性
DOI：
10.1021/acs.jpcb.9b00449
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Wheeler, Ralph A.
中科院分区：
文献类型：
--
作者：
Mackoy, Travis;Mauro, Nicholas A.;Wheeler, Ralph A.
许多离子液体的静态结构因子（S（q））显示出低波数峰，其强度随温度的升高而增加。更大的峰强度似乎意味着随着温度的升高，中程有序度增加。离子液体1-丁基-1-甲基吡咯烷鎓双盐的分子动力学模拟三氟甲磺酰亚胺（C_4C_1pyrrTFSI）计算S（q）和偏S（q）。（阳离子-阳离子，阴离子-阴离子，阳离子-阴离子）在298，363，S（q）和偏S（q）进一步分解为正负分量（其各自指示结构排序）通过分别对正和负傅立叶变换被加数求和。温度升高会导致每个偏S（q）的负分量的幅度比正分量的幅度减小得更多，从而导致totalS（q）的幅度增加。因此，结构有序与周期对应的观察到的峰在S（q）不增加，而是退相干随着温度的增加，即使S（q）峰高增加。傅立叶变换和也显示了当温度增加时，在真实的空间中，正分量和负分量对S（q）的贡献改变的位置。这种新的，详细的分析的基础上傅立叶变换summands spectrosingS（q）主张非常谨慎时，解释S（q）的强度，并强调模拟的价值作为补充X射线（或中子）散射实验。
Static structure factors (S(q)) for many ionic liquids show low-wavenumber peaks whose intensities increase with increasing temperature. The greater peak intensities might seem to imply increasing intermediate-range order with increasing temperature. Molecular dynamics (MD) simulations for a representative ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (C4C1pyrrTFSI), were used to calculateS(q) and partialS(q) (cation–cation, anion–anion, and cation–anion) at 298, 363, and 500 K.S(q) and partialS(q) were further decomposed into positive and negative components (which each indicate structural ordering) by separately summing positive and negative Fourier transform summands. Increasing temperature causes the negative components of each partialS(q) to decrease in magnitude more than the positive components, causing the totalS(q) to increase in magnitude. Thus, structural ordering with periodicities corresponding to observed peaks inS(q) does not increase but instead decoheres with increasing temperature, even thoughS(q) peak heights increase. Fourier transform summands also show where in real space the positive and negative component contributions toS(q) change when the temperature increases. This new, detailed analysis based on Fourier transform summands comprisingS(q) argues for great caution when interpretingS(q) intensities and highlights the value of simulations as a complement to X-ray (or neutron) scattering experiments.