Effect of blending on the PVME dynamics. A dielectric, NMR, and QENS investigation

In this work we have investigated how the dynamics of poly(vinyl methyl eth er), PVME, changes by blending with deuterated polystyrene. The experimenta l techniques used were dielectric spectroscopy, quasielastic neutron scatte ring, and C-13 nuclear magnetic resonance. By means of these techniques, th e dynamics of the poly(vinyl methyl ether) units in the blends can be selec tively investigated in a huge time range (10(1)-10(-11) s). Two different b lend compositions have been investigated. The main relaxation processes obs erved in this range are the secondary beta-process and the segmental alpha- relaxation. It turns out that the beta-relaxation is not affected by blendi ng. The data analysis procedure followed by us in the case of the alpha-pro cess is based on the assumption that the dynamics of the PVME segments in t he blends is a superposition of dynamical processes with the same shape as that in pure PVME, but with the relaxation times distributed due to the pre sence of concentration fluctuations. From this analysis we found that, in t he blends, and in pure PVME as well, the results obtained by means of the d ifferent techniques can consistently be described with the same set of para meters. Moreover, the temperature dependence of the distribution of relaxat ion times in each blend composition can be accounted for by a single, tempe rature-independent, Gaussian distribution of the Vogel-Fulcher temperature, T-0, the average and the variance of the distribution increasing as the PV ME concentration decreases. Our results suggest that a significant number o f PVME segments in the blends move faster than in pure PVME. Furthermore, o ur results strongly indicate that each polymer component of the blend exhib its very different alpha-relaxation rates, i.e., different "glass transitio ns". Several implications of these results concerning the usually accepted ideas of polymer blend dynamics are outlined.