Dynamics of PEO in blends with PMMA: Study of the effects of blend composition via quasi-elastic neutron scattering

We address the dynamic behavior of poly(ethylene oxide) [PEO] in miscible blends with poly(methyl methacrylate). [PMMA] by using quasi-elastic neutron scattering [QENS] with isotopic labeling. The data reveal two dynamic processes in the picosecond-nanosecond time scales: a slow process that is consistent with previous measurements of the segmental relaxation and a composition independent fast process occurring on the picosecond time scale. The composition dependence of the slow process differs from previous measurements, particularly at low PEO content. The fast process is similar to the fast process observed in pure polymers and is insensitive to blending with PMMA. Relaxation times extracted from Kolraush-Williarns-Watts [KWW] fits to the data are used to test the applicability of the chain connectivity and coupling models as a function of spatial scale. Both models describe slow process relaxation times within a small range of spatial scales near the Kuhn length of PEO. The effective concentration, when obtained as a fit parameter in chain connectivity model fits, is not a constant, but it decreases with increasing spatial scale.