Recent neutron scattering and related results from simulation and other techniques on the microscopic dynamics of polymers under confinement are presented. Coexistence of dynamical phases in the confined polymer determines the macroscopic properties.

The macro- and microstructural evolution of water swollen and ethanol swollen regenerated cellulose gel beads have been determined during drying by optical microscopy combined with analytical balance measurements, small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS). Two characteristic length scales, which are related to the molecular dimension of cellulose monomer and elongated aggregates of these monomers, could be identified for both types of beads by SAXS. For ethanol swollen beads, only small changes to the structures were detected in both the SAXS and WAXS measurements during the entire drying process. However, the drying of cellulose from water follows a more complex process when compared to drying from ethanol. As water swollen beads dried, they went through a structural transition where elongated structures changed to spherical structures and their dimensions increased from 3.6 to 13.5 nm. After complete drying from water, the nanostructures were characterized as a combination of rodlike structures with an approximate size of cellulose monomers (0.5 nm), and spherical aggregates (13.5 nm) without any indication of heterogeneous meso- or microporosity. In addition, WAXS shows that cellulose II hydrate structure appears and transforms to cellulose II during water evaporation, however it is not possible to determine the degree of crystallinity of the beads from the present measurements. This work sheds lights on the structural changes that occur within regenerated cellulose materials during drying and can aid in the design and application of cellulosic materials as fibers, adhesives, and membranes.

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Using high resolution PFG NMR spectroscopy, we have studied the diffusion of well-characterized polymer rings in linear host matrices at various observation times Δ, varying both ring and host molecular weights. For the first time, to our knowledge, for higher M w rings in entangled melts it was possible to directly distinguish two different diffusive modes: (i) fast diffusion that scales inversely with the host chain length and (ii) much slower diffusion depending much more strongly on the host molecular weight. Furthermore, we studied the diffusion of the linear chains in the host melts. The diffusion data were analyzed in terms of existing theories and compared to simulations. The two-mode structure directly verifies the hypothesis of qualitatively different mechanisms for ring diffusion in linear melts. The fast mode quantitatively agrees with the assertion of a special diffusion channel for once threaded rings, while the suggested diffusion of unthreaded rings was not found. The slow mode scales more weakly with the host chain length than predicted by the constraint release (CR) mechanism. However, considering an interdependence of constraints (Macromolecules 1986, 19, 105), the slow mode was quantitatively related to tube renewal processes. Using this concept also the molecular weight dependence of the matrix diffusion is described naturally. In contrast to the explicit observation of fast and slow diffusive modes simulations reveal broadly distributed heterogeneities leading to a prevailing CR mechanism only. The strong size dependent ring diffusion in an entangled matrix remains unintelligible. Finally, even though we have distinguished two well-defined significantly different diffusive modes with characteristic times in the millisecond range that would be expected to interchange, a detailed analysis in terms of a two-state diffusion model allowing for state changes reveals that within the experimental sensitivity no such exchanges take place.