Composition and Long-Range Density Fluctuations in PEO/PMMA Polymer Blends: A Result of Asymmetric Component Mobility

Fluctuations of density and composition were observed in the disordered regime of a symmetric poly(ethylene oxide) (PEO) and a poly(methyl methacrylate) (PMMA) polymer blend. This blend is of particular interest as the glass transition (T-G) of both polymers happens at very different temperatures thereby inducing a dynamic asymmetry in the molecular dynamics. Small-angle neutron scattering and oscillatory shear rheology were the principle experimental tools. Composition fluctuations determined the Flory-Huggins parameter as well as glass and gelation temperature (T-A). The density fluctuations are of long-range and show a mass fractal dimension whose strength enlarges below the glass transition. A fairly constant T-A about 40 K above T-G separates two regions of distinctively different fluctuation behavior. A comparison of viscoelastic plateau modulus and high frequency modulus determined from rheology and SANS show that the relaxation modes in the regime between T-G and T-A are determined by the freezing segmental modes of PMMA.