Solvent and polymer dynamics in concentrated polystyrene/toluene solutions

Abstract

Depolarized Rayleigh scattering (DRS) and dielectric spectroscopy (DS) are employed to study the solvent and polymer dynamics in the polystyrene (PS)/toluene system and for PS concentration up to 0.6 g/ml. The DRS measurements were made in the temperature range from 255 to 373 K with different interferometers making possible the separation of the ‘‘fast’’ solvent (in the ps time scale) from the ‘‘slow’’ polymer dynamics (in the ns time scale). The DS measurements were made in the temperature range from 128 to 310 K and two processes could also be observed. With DRS and DS we investigate the very different mobilities in the PS/toluene solutions over a frequency range of ∼10 decades. The prominent features of the experimental data are (i) the existence of two primary (α−) relaxations in the macroscopically homogeneous solutions which have been analyzed using both techniques and (ii) that these relaxations reflect the polymer and solvent dynamics and display the usual Vogel–Fulcher–Tammann behavior, however, with a broad distribution of relaxation times, especially at low temperatures. The existence of two time scales in the solutions is discussed in terms of concentration heterogeneities composed of PS-rich and toluene-rich domains, large enough to exhibit two glass transitions. As a result of the strong temperature dependence for the fast solvent reorientation times the rate of change of solvent friction with polymer concentration becomes temperature dependent at low temperatures.