Understanding Thermal Diffusion in Liquid Mixtures and Macromolecular Solutions via Molecular Dynamics Simulations

该项目的目的是通过分子动力学模拟进一步深入了解流体混合物中热扩散（Soret效应）的分子起源。在Lennard-Jones液体混合物的现有经验的基础上，将进行两方面的研究。首先，将模拟扩展到现实的液体混合物的原子模型。其目的是将结果与最近可用或正在进行的精确测量进行比较，从而定量验证分子动力学方法。这将使我们能够检查，如果从早期的工作中得到的概念伦纳-琼斯模型的混合物，如索雷特效应的质量和内聚能密度的差异的可加性，仍然保持在现实的系统。详细的原子模拟的另一个目的是理解Köhler等人最近的实验发现，即Soret效应也具有由部件的惯性矩的差异引起的贡献。其次，模拟是进行简单的模型链状低聚物的解决方案（珠弹簧型高分子在单原子溶剂）。这组模拟的目的是在研究的特点Soret效应在大分子溶液中，特别是独立的热扩散系数的链长和符号反转的Soret系数与溶剂质量的变化。这些效应是相当普遍的，并且已经在许多大分子溶液中发现。因此，最初使用简化的低聚物模型是明智的，它允许模拟大型系统。大型系统是必要的，因为这些溶液非常稀，所以必须包括许多明确的溶剂。这两种模拟方法都将与PD Dr. Simone Wiegand（FZ Jülich）的实验组密切合作执行。

The aim of the proposed project is to gain further insight into the molecular origin of thermal diffusion (Soret effect) in fluid mixtures by means of molecular dynamics simulations. Building on existing experiences gained on mixtures of Lennard- Jones liquids, two lines of research are to be pursued. Firstly, the simulations are to be extended to realistic atomistic models of liquid mixtures. The purpose of this is to compare results with accurate measurements, which recently have become available or are being conducted, and to thereby validate the molecular dynamics approach quantitatively. This will allow us to check if concepts derived from the earlier work on Lennard-Jones model mixtures, such as the additivity of Soret effects from the differences in mass and in cohesive energy density, still hold in realistic systems. Another purpose of the detailed atomistic simulations is to understand a recent experimental finding by Köhler et al., namely that the Soret effect also has a contribution arising from the difference of moments of inertia of the components. Secondly, simulations are to be conducted with simple models of chain-like oligomer solutions (bead-spring type macromolecule in a monoatomic solvent). This set of simulations is aimed at studying the peculiarities of the Soret effect in macromolecular solutions, in particular the independence of the thermal diffusion coefficient of the chain length and the sign reversal of the Soret coefficient with changing solvent quality. These effects are quite generic and have been found for many macromolecular solutions. It is therefore sensible to initially use a simplified oligomer model, which allows the simulation of large systems. Large sys- tems are necessary, as these solutions are very dilute, so much explicit solvent has to be included. Both simulation approaches will be executed in close collaboration with the experimental group of PD Dr. Simone Wiegand (FZ Jülich).