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

• Applicant: Professor Dr. Florian Müller-Plathe
• Subject Area: Experimental and Theoretical Physics of Polymers
• Term: from 2004 to 2011
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5442127

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).

• DFG Programme: Research Grants
• Participating Person: Privatdozentin Dr. Simone Wiegand