Collective motion in Poly(ethylene oxide)/poly(methylmethacrylate) blends

We present neutron spin echo and structural measurements on a perdeutereted miscible polymer blend: poly(ethylene oxide)[PEO]/poly(methyl methacrylate)[PMMA], characterized by a large difference in component glass transition temperatures and minimal interactions. The measurements cover the q range 0.35 to 1.66 A(-1) and the temperature range T-g-75 to T-g+89 K, where T-g is the blend glass transition. The spectra, obtained directly in the time domain, are very broad with stretching parameters beta similar to 0.30. The relaxation times vary considerably over the spatial range considered however at none of the q values do we see two distinct relaxation times. At small spatial scales relaxations are still detectable at temperatures far below T-g. The temperature dependence of these relaxation times strongly resembles the beta-relaxation process observed in pure PMMA.