Dynamic Confinement Effects in Polymer Blends. A Quasielastic Neutron Scattering Study of the Dynamics of Poly(ethylene oxide) in a Blend with Poly(vinyl acetate)

Quasielastic neutron scattering combined with deuteration labeling has allowed us to follow selectively the dynamics of the hydrogens of poly(ethylene oxide) (PEO, T g ≈ 220 K) in a blend with poly(vinyl acetate) (PVAc, T g = 315 K) (20% PEO/80% PVAc in weight, = 280 K). Temperatures between −10 K and + 120 K have been explored by backscattering techniques, accessing a dynamical window centered on the nanosecond range and with momentum transfers Q in the inter- and intrachain region. Two essentially different dynamical behaviors have been identified for PEO in the blend: (i) at high temperatures (≈ + 100 K) the dynamics is not qualitatively different from that of a glass-forming homopolymer (regarding spectral shape and dispersion of the time scales); (ii) close to, extremely broad distributions of relaxation times are found that do not depend on Q in the high- Q range, strongly suggesting localized dynamics. Apparently, the slowing down of the motions in the PVAc component toward leads to the confinement of PEO dynamics on small length scales. As soon as the dynamics of the more rigid polymer becomes fast enough to allow PEO long-range relaxations (≈ T g + 80 K), the fast component reaches a situation of certain equilibrium, at least for length scales of the order of a nanometer. Our results perfectly agree with those reported for PEO in a blend with poly(methyl methacrylate) [Genix et al. Phys. Rev. E 2005, 72, 031808]. The confined processes in both “rigid environments” show nearly identical features. In addition, neutron diffraction experiments with polarization analysis indicate that, while blending hardly affects the short-range order of PVAc chains, it leads to larger and more distributed characteristic distances involving PEO segments.