Collective and thermal diffusion in dilute, semidilute, and concentrated solutions of polystyrene in toluene

Collective mass diffusion (D), thermal diffusion (D-T), and Soret coefficients (S-T) have been determined for solutions of polystyrene in toluene ranging from dilute (10(-4) g/cm(3)) to concentrated (0.9 g/cm3) by a transient holographic grating technique and photon correlation spectroscopy (collective diffusion only). The molar mass range of the polymer was between 4.75 and 4060 kg/mol. With a slight exception at intermediate concentrations, D-T is molar mass independent over the entire concentration range. Above a polymer concentration of Capproximate to0.2 g/cm(3) the rising glass transition temperature of the solution leads to a rapid slowing down of both mass and thermal diffusion (Ludwig Soret effect) and the structure relaxation enters the experimental time window. Both D and D-T are governed by the same microscopic local viscosity eta(eff), which increases dramatically at T-g. It cancels out in S-T=D-T/D. As a consequence, S-T is completely insensitive to the glass transition and shows concentration-dependent scaling as expected for a fictive polymer solution with concentration-independent local friction. Where available, results are compared with literature data. (C) 2003 American Institute of Physics.