DIELECTRIC STUDIES OF THE ALPHA-RELAXATION IN MISCIBLE POLYMER BLENDS AND ITS RELATION TO CONCENTRATION FLUCTUATIONS

The alpha-relaxations in homogeneous polymer blends are often compared with the corresponding relaxations in their pure components, an effect that has long been associated qualitatively with concentration fluctuations. A novel ''fluctuation model'' describes very accurately the observed dielectric relaxation curves measured in polyvinylmethylether/polystyrene. From this analysis of measured alpha-relaxations the mean square concentration fluctuations [(deltaphi)2] can be evaluated as functions of temperature and average concentration phi0. In the description of concentration fluctuations in terms of the well-known random phase approximation, the relevant parameter for the temperature dependence of [(deltaphi)2] is the reference volume element V. For fluctuations calculated from the dielectric alpha-relaxation this volume was found to be identical with a ''cooperatively rearranging domain'' which has been discussed in theoretical treatments concerning the glass transition.