title: Unusual thermal diffusion in polymer solutions.
abstract: Thermal diffusion forced Rayleigh scattering results on thermal diffusion of poly(ethylene oxide) (PEO) in ethanol/water mixtures are presented. In water-rich solvent mixtures, PEO is found to migrate towards regions of lower temperature. This is typical for polymer solutions and corresponds to a positive Soret coefficient of PEO. In solvent mixtures with low water content, however, the polymer is found to migrate towards higher temperatures, corresponding to a negative Soret coefficient of PEO in ethanol-rich solutions. To our knowledge, this is the first observed sign change of the Soret coefficient of a polymer in solution. We also present a simple lattice model for the polymer solvent system and calculate Soret coefficients with statistical mechanics methods. The calculated values agree qualitatively with the experimental results.
authors.affiliation: Max Planck Institut für Polymerforschung, Ackermannweg 10, D-55128 Mainz, Germany. bjdegans@gmx.de
authors.forename: Berend-Jan
authors.initials: BJ
authors.lastname: de Gans
authors.forename: Rio
authors.initials: R
authors.lastname: Kita
authors.forename: Simone
authors.initials: S
authors.lastname: Wiegand
authors.forename: Jutta
authors.initials: J
authors.lastname: Luettmer-Strathmann