SPP 1369, Teilprojekt: Polymere Interphasen in selbstgeordnetem porösem Aluminiumoxid: NMR-Untersuchung der Kettendynamik

The nanoscopic confinement effect of hard neutral or attractive walls on the dynamics of polymer chains in the melt is studied by solid-state NMR. We apply a variety of NMR techniques to the characterization and the elucidation of chain dynamics in true model composites based on self-ordered nanoporous alumina with well-defined geometry and the possibility to tune the properties of the inorganic surface. In close collaboration with other projects employing neutron scattering, field-cycling NMR, and computer simulations , we focus on the local segmental modes as well as on larger-scale reptation motions, with particular emphasis on their anisotropy. In the first funding period, we found that the long-time dynamics of entangled melts is significantly different from the bulk and rather anisotropic in a layer of a few nm close to the weakly interacting wall, and that the effect appears to scale with the entanglement spacing. Further preliminary studies demonstrated that these effects are orientation dependent, and also occur for nominally unentangled melts. We also studied the large-scale diffusion by pulsed-gradient NMR and the infiltration kinetics by confocal fluorescence microscopy, and successfully conducted first pore-wall modification experiments. For the second funding period, we plan to extend the initial studies by comparing polymers with different entanglement spacings, focus at the effects of pore-wall polarity on the dynamics, develop a quantitative understanding of the anisotropy of the effects via angle-dependent experiments, and finally implement spin-diffusion experiments to study property gradients.