Dynamic heterogeneity in a miscible poly(vinyl acetate)/poly(ethylene oxide) blend

We studied viscoelastic and dielectric relaxation behavior of poly(vinyl acetate)/poly(ethylene oxide) (PVAc/PEO) blends in the miscible state. Especially for the viscoelastic measurements, we used highly asymmetric molecular weight MW combinations to examine the component dynamics separately. Time–temperature superposition principle did not hold since the two components have different shift factors (aT). We determined the aT of both components in the blends for the terminal relaxation modes. Concerning the dielectric relaxation, we observed single α-relaxation peak and found that the α-relaxation mainly reflected the segmental motion of PVAc in the blends. The dielectric and viscoelastic aT of the PVAc component showed almost the same temperature dependence compared at the same composition. From these aT data, we determined effective glass transition temperatures (Tg,eff) as a function of blend composition for both components. The results were compared with the literature data for a similar miscible blend, poly(methyl methacrylate) (PMMA)/PEO [T.R. Lutz, Y. He, M.D. Ediger, H. Cao, G.Lin, A.A. Jones, Macromolecules 36 (2003) 1724]. The Tg,eff’s of PEO in the two blend systems were almost the same at any compositions even though the blend partners have very different glass transition temperatures Tg’s: 311 K for PVAc and 405 K for PMMA. If we use the Lodge–McLeish (LM) model to explain the similar Tg,eff’s of PEO in both blends, the self-concentration of PEO should be dependent on the blend partner. This suggests the necessity to take into account the effect of the inter-molecular interaction in the LM model.