Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 20: POSTERS Driven Soft Matter
CPP 20.14: Poster
Mittwoch, 27. Februar 2008, 16:00–18:30, Poster A
The crossover of transport properties of polymer solutions from the high polymer limit to finite chain length — •Dominik Stadelmaier, Jürgen Rauch, Marianne Hartung, and Werner Köhler — Physikalisches Institut, Universität Bayreuth
In our contribution we discuss the influence of polymer chain length and solvent viscosity on the Soret effect in polymer solutions. The Soret effect (thermal diffusion) describes the mass flow in a binary system with a temperature gradient. In most polymer solutions the polymer is moving to the cold side (thermal diffusion coefficient DT is positive) and DT does not depend on the polymer chain length in the high polymer limit as already recognized by de Gennes in 1981 and observed in previous experiments. This suggests to interpret DT as being a property of the monomer. Measurements of long chained polystyrene (PS) in different solvents in our group have identified the viscosity as the dominating solvent parameter. In order to investigate the crossover from the polymer regime to shorter chains we measured samples of polystyrene solutions with molar masses ranging from 4·103 kg/mol down to the effective monomer ethylbenzene. Remarkably DT decreases with decreasing polymer chain length but remains positive for all solvents down to the dimer. For the effective monomer there is a sign reversal in three of the solvents. Our results suggest an interpretation for DT in terms of effective correlated segments acting as thermodiffusing entities that are much larger than a single monomer unit and approximately of the size of the Kuhn segment.