X-ray Diffraction Analysis of Poly(vinyl alcohol) Hydrogels, Obtained by Freezing and Thawing Techniques

作者：Rosa Ricciardi, Finizia Auriemma, Claudio De Rosa, F. Lauprêtre · 发表于：Macromolecules · 年份：2004 · DOI：10.1021/ma035663q · 被引用次数：783 · 研究领域：Hydrogels: synthesis, properties, applications、Advanced Sensor and Energy Harvesting Materials、Polymer Nanocomposite Synthesis and Irradiation

The structure of physical poly(vinyl alcohol) (PVA) hydrogels prepared by subjecting a PVA/D 2 O 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 swollen amorphous PVA while the crystalline domains act as knots of the gel network. The presence of crystalline knots ensures a high dimensional stability of the gel and induces elastic properties. Long time aging in sealed vials at room temperature induces large variations in the structure of freeze/thaw PVA hydrogels. The porous structure formed during freeze/thaw cycles in PVA hydrogels, instead, is not greatly altered upon drying and during the successive rehydration step; r...