Composition dependence of segmental dynamics of poly(methyl methacrylate) in miscible blends with poly(ethylene oxide)

We investigate the composition dependence of the segmental dynamics of poly(methyl methacrylate) [PMMA] in miscible binary blends with poly(ethylene oxide) [PEO] using quasi-elastic neutron scattering [QENS] in combination with deuterium labeling. Blends with 10, 20, and 30 wt % PEO are considered. Our main finding is that in all cases the segmental mobility of PMMA is controlled simply by the distance above the glass transition temperature. This holds for pure PMMA and all three blends and at all spatial scales over the 4-10 Å range of observation. The best fits to the chain connectivity model are obtained with a self-concentration of zero, indicating that the local "effective" concentration defined over length scales comparable to our experiment is equal to the bulk composition. This is again consistent with segmental dynamics that follow the bulk [mixture] composition. Within the temperature range measured, the relaxation times are consistent with Arrhenius behavior: the resulting activation energy is independent of composition and consistent with that obtained from dielectric spectroscopy for the merged αβ-process of pure PMMA.