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The structure of physical poly(vinyl alcohol) (PVA) hydrogels prepared by subjecting a PVA/D2O solution (11% w/w PVA) to freeze (−22 °C)/thaw (+25 °C) cycles has been systematically investigated by X-ray powder diffraction technique as a function of the number of cycles and aging time. The structural analysis has been extended to PVA “dried gels” and PVA hydrogels obtained by rehydrating the dried samples. The results of the present analysis confirm that highly stable PVA hydrogels, with a water uptake higher than 80%, may be obtained upon freeze/thaw cycles. The X-ray diffraction profiles of PVA hydrogels have been interpreted in terms of three components: “free water”, crystalline PVA aggregates, and swollen amorphous PVA. The degree of crystallinity and the size of the crystals increase with increasing the number of freeze/thaw cycles and the aging time. Our results support the hypothesis that PVA hydrogels have a porous structure, with pores mainly occupied by water. The porous walls consist of swoll...

Molecular dynamics simulations were employed in bulk polyisobutylene, to provide a detailed characterization of the methyl dynamics and to examine its relation to the β-relaxation as described by different experimental techniques. The simulation results were compared to new 13C NMR measurements probing methyl motion at temperatures above the glass transition, as well as to lower temperature literature NMR data. It was found that the 13C NMR results, and those for the β-relaxation reported by dielectric relaxation spectroscopy and neutron scattering experiments, can be interpreted on a common basis through a coupling mechanism between methyl rotation and a recently described fast relaxation motion associated with the chain backbone. In addition, a molecular mechanism for the description of the dielectric β-process observed in polyisobutylene is proposed, and investigated by simulations.