Structural changes of water in poly(vinyl alcohol) hydrogel during dehydration

Kudo, Kushi*; Ishida, Junichi*; Syuu, G.*; Sekine, Yurina   ; Fukazawa, Tomoko*

To investigate the mechanism of structural changes of water and polymer networks with drying and swelling, we measured the Raman spectra of a physically cross-linked poly(vinyl alcohol) (PVA) hydrogel synthesized using the freezing thawing method. On the basis of the dependence of the frequency shifts on the PVA concentration of the original solution, it was found that the structure of the polymer network in the reswollen hydrogel becomes inhomogeneous due to shrinkage of the polymer network with drying. Furthermore, to investigate the effects of the cross-linking structure on the drying process, these results were compared with those of a chemically cross-linked PVA hydrogel synthesized using glutaraldehyde as a cross-linker. The results show that the structures of the polymer network and water change with the gel preparation process, cross-linking method, and drying and reswelling processes.