Dresden 2009 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 15: POSTERS Dynamics and Diffusion
CPP 15.7: Poster
Tuesday, March 24, 2009, 14:00–16:30, P3
From Monomers to Polymers: Correlated Segments in Diffusive Transport — •Dominik Stadelmaier and Werner Köhler — Universität Bayreuth, Physikalisches Institut
We have performed measurements on dilute polymer and alkane solutions to investigate the influence of the polymer stiffness on the Soret effect. The Soret effect (thermal diffusion) describes the mass flow in a binary system with a temperature gradient. In the high polymer limit the thermal diffusion coefficient is - contrary to the long-range hydrodynamic coupling in case of isothermal diffusion - independent of the polymer chain length. For polystyrene, thermal diffusion mainly depends on a factor proportional to the correlated segment size and on the solvent viscosity [1]. Measurements with the flexible polymers PDMS and polyethylen-oligomers however show that the solvent viscosity is no longer the only relevant solvent parameter for the Soret effect. Even a sign change is possible if the solvent viscosity is increased. For the measured alkane solutions DT is always negative thus the alkane molecules are more thermophilic than the solvent. But the crossover from a small molecule to a molecule with polymer properties always takes place at a chain length that is approximately of the size of the Kuhn segment.
[1] Stadelmaier D., Köhler W., Macromolecules 41, (2008), 6205