Investigation of the relationships between the chain organization and rheological properties of atactic poly(vinyl alcohol) hydrogels |
| |
Authors: | Rosa RicciardiChristine Gaillet Guylaine DucouretFrançoise Lafuma Françoise Lauprêtre |
| |
Affiliation: | a Laboratoire de Recherche sur les Polymères, UMR 7581-CNRS, 2 à 8 rue Henri Dunant, 94320 Thiais, France b Laboratoire de Physicochimie Macromoléculaire, ESPCI, 10 rue Vauquelin, 75231 Paris cedex 05, France |
| |
Abstract: | The structure and rheological behavior of atactic poly(vinyl alcohol) (a-PVA) hydrogels prepared by freeze/thaw cycles were investigated as a function of polymer concentration and number of freeze/thaw cycles. The presence of phases with different mobilities was observed using 13C CP/MAS and DP/MAS NMR experiments. The degree of crystallinity of the a-PVA-rich phase was determined by 1H NMR free decay experiments. Measurements of the shear storage and loss modulus were performed at a fixed frequency of 1 Hz and a strain value of 0.1%, i.e. under conditions where the deformation imposed on the gel structure is entirely reversible. Results thus obtained showed that an increase in the number of freeze/thaw cycles induces an increase in the degree of crystallinity in the polymer-rich phase together with an increase in the storage modulus. The a-PVA hydrogels became more fragile as the number of freeze/thaw cycles was increased. Moreover, both the percentage of protons in a rigid environment measured by 1H NMR and the storage modulus values tended to a limiting value after six freeze/thaw cycles. These results show that the first five or six freeze/thaw cycles play a very important role in determining the hydrogel structure and rheological properties. A more detailed comparison of NMR and rheological data led to the conclusion that the storage modulus is mainly controlled by the a-PVA crystallinity while the hydrogen bond interactions have a much smaller contribution. |
| |
Keywords: | Poly(vinyl alcohol) hydrogels NMR Rheology |
本文献已被 ScienceDirect 等数据库收录! |
|