We report on the preparation and characterization of poly(vinyl alcohol) (PVA) hydrogels formed during freeze−thaw (F−T) cycles of their aqueous solutions containing γ-cyclodextrin (γ-CD). Crystalline inclusion compound (IC) formation was observed between PVA and γ-CD in these gels at low concentrations of γ-CD (γ-CD:PVA molar ratios < 1:25). Confirmation of the existence of the channel structure for γ-CD was achieved by characterizing the dried PVA/γ-CD hydrogels with solid-state DSC, TGA, WAXD, and 13 C NMR. Some aspects regarding the mechanism and structure of PVA gels obtained via F−T cycles in the presence/absence of γ-CD are presented based on UV−vis, swelling, solution 1 H NMR, and rheological observations. It was observed that the swelling and rheological responses of the aqueous PVA gels formed during F−T cycles in the presence of γ-CD can be controlled by adjustment of the PVA:γ-CD molar ratio employed during their gelation.
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Hernández et al. (2004) studied this question.
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