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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Molecular Dynamics Study of Dielectric Properties of Water-Dimethyl Sulfoxide Mixtures
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Molecular Dynamics Study of Dielectric Properties of Water-Dimethyl Sulfoxide Mixtures

机译：水-二甲基亚砜混合物介电性能的分子动力学研究

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摘要

Both the static and dynamic dielectric properties of water-dimethyl sulfoxide (DMSO) mixtures over the whole composition range are investigated by means of molecular dynamics (MD) simulations, and the results are compared with available experimental measurements. We discuss the behavior of the dielectric constant and Kirkwood dipole correlation factor as functions of composition in terms of the self- and cross-species dipole density correlations and a suitable set of real space dipole-dipole distribution functions. We find that short-ranged structural correlations between neighboring water and DMSO molecules strongly influence the system's static dielectric properties, as expected on the basis of the molecular associations these mixtures are known to exhibit. In terms of the dynamics, we report time correlation functions for the mixtures' dipole densities and find that their long-time behavior can be reasonably well described by either biexponential or stretched exponential decays, which means that the dielectric relaxations of these mixtures are governed by complex, multi time scale mechanisms of rotational diffusion. The dipole density relaxation time is a nonmonotonic function of composition passing through a maximum around 33% mole DMSO, in agreement with the experimental data for the mixtures' main dielectric relaxation time. Frequency-domain results such as the frequency spectra of the single-dipole time correlations and the experimentally accessible far-infrared absorption coefficient reveal that mixing also exerts a profound effect upon the librational dynamics of water molecules. This effect is much stronger than and qualitatively different from that observed in other associating aqueous mixtures and has been examined in view of new DMSO-water molecular aggregates suggested in previous MD works.
机译：通过分子动力学（MD）模拟研究了水-二甲基亚砜（DMSO）混合物在整个组成范围内的静态和动态介电性能，并将结果与​​可用的实验测量进行了比较。我们根据自物种和跨物种的偶极子密度相关性和一组合适的实际空间偶极子-偶极子分布函数，讨论介电常数和柯克伍德偶极子相关因子作为组成函数的行为。我们发现，相邻水和DMSO分子之间的短程结构相关性强烈影响系统的静态介电性能，这是基于已知这些混合物表现出的分子缔合关系所期望的。在动力学方面，我们报告了混合物的偶极密度的时间相关函数，发现它们的长期行为可以通过双指数或拉伸指数衰减来很好地描述，这意味着这些混合物的介电弛豫由复杂的，多时间尺度的旋转扩散机制。偶极子密度弛豫时间是通过最大约33％摩尔DMSO的组合物的非单调函数，与混合物主要介电弛豫时间的实验数据一致。频域结果（例如单偶极时间相关性的频谱和实验可访问的远红外吸收系数）表明，混合还对水分子的释放动力学产生了深远的影响。这种效果比其他缔合的水性混合物要强得多，并且在质上也有所不同，并且已经考虑到以前的医学博士工作中提出的新型DMSO-水分子聚集体的作用。

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