Experimental study of the thermal diffusion behaviour of mixtures consisting of simple and chain-like molecules

我们计划系统测量刚性和链状分子混合物的热扩散行为（Soret效应），有或没有特定的相互作用。目标是获得对热扩散过程更好的微观理解。数据将通过全息光栅技术，即所谓的热扩散强迫瑞利散射（TDFRS）来获得。我们想研究三组低分子量混合物：刚性分子、链状分子和具有特定相互作用的分子。所有实验将与Florian m<s:1> ller- plathe教授（不来梅大学）的理论小组密切合作，参见他在这个串联应用程序中的部分。首先，我们希望通过研究刚性低分子量分子，例如四面体或环状分子，来了解质量和转动惯量对Soret系数的影响。重点应该放在没有氢键等特殊相互作用的系统上。为了研究质量和转动惯量的影响，应使用氘化溶剂。还应研究体系的浓度和温度依赖性。此外，还应研究构象变化的影响。其次，我们想研究在聚合物溶液中观察到的热扩散系数DT对链长的独立性是否仍然适用于低聚物溶液和定义良好的链状分子。它们比低聚物定义得更好，低聚物通常在端基和结构上有所不同。还计划对低聚物进行系统测量，以检查是否有可能找到描述不同链长低聚物的Soret系数ST的一般表达式。最后，我们希望将我们的研究扩展到具有氢键等特定相互作用的系统。我们主要关注的是水溶液。我们想研究质量、溶剂质量和特定相互作用（如氢键）对热扩散过程的影响。一个特别感兴趣的系统是乙醇/水中的乙二醇（EG）。对于聚乙二醇，我们观察到索莱特系数随溶剂组成的函数有一个符号变化。系统地研究分子质量、浓度依赖关系以及在氘化溶剂混合物中的研究，有助于深入了解热扩散过程的微观机理。计算机模拟将伴随实验，以便在微观水平上理解这一过程。

We plan systematic measurements on the thermal diffusion behaviour (Soret effect) in mixtures of rigid and chain-like molecules with and without specific interactions. The goal is to gain a better microscopic understanding of the thermal diffusive process. The data will be obtained by means of a holographic grating technique the so-called thermal diffusion forced Rayleigh scattering (TDFRS). We want to study three groups of low molecular weight mixtures: Rigid molecules, chain-like molecules and molecules with specific interactions. All experiments will be executed in close collaboration with the theoretical group of Prof. Dr. Florian Müller-Plathe (IU Bremen), see his part in this tandem application. First, we want to gain insight in the influence of mass and the moment of inertia on the Soret coefficient by studying stiff low molecular weight molecules, e.g. tetrahedral or ring shaped. The focus should be on systems with no specific interactions as hydrogen bonds. Deuterated solvents should be used in order to study the influence of mass and moment of inertia. The concentration and temperature dependence of the systems should also be studied. Furthermore the influence of conformational changes should be studied. Secondly, we want to study whether the independence of the thermal diffusion coefficient DT on the chain length, which has been observed for polymer solutions is still valid for oligomer solutions and for well-defined chain like molecules. These are better defined than oligomers, which often differ in end group and structure. Systematic measurements are also planned for oligomers to check whether it is possible to find a general expression for the Soret coefficient ST which describes oligomers of different chain length. Finally, we want to extend our study to systems with specific interactions as hydrogen bonds. Our main focus is on aqueous solutions. We want to investigate the influence of the mass, the solvent quality and specific interactions, such as hydrogen bonds on the thermal diffusive process. One particular system of interest is ethylene glycol (EG) in ethanol/water. For poly(ethylene glycol), one observes a sign change of the Soret coefficient as function of solvent composition. Systematic studies of the molecular weight, concentration dependence and the study in the deuterated solvent mixture should give insight in the microscopicmechanism of the thermal diffusion process. Computer simulations will accompany the experiments in order to understand the process at the mi- croscopic level.