Swelling and viscoelastic properties of poly(vinyl alcohol) physical gels synthesized using sodium silicate

A physically crosslinked poly(vinyl alcohol) (PVA) gel was synthesized from mixed aqueous solutions of PVA and sodium silicate (SS) using freeze/thaw techniques. The infrared spectroscopy, swelling and viscoelastic properties of the resultant gel have been investigated. The infrared spectrum of the resultant gel was as in the spectrum of PVA gel without SS. The resultant gel showed that the absorbing band due to stretching of hydroxyl groups shifted to a lower wave number, indicating the enhancement of hydrogen bonding between hydroxyl groups in PVA. Dynamic viscoelastic measurements showed that the storage modulus of the resultant gel was 1 order of magnitude higher than that of PVA gel without SS. The degree of swelling Q varied with the SS concentration cSS as Q∼cSS-ν (0.12 < ν < 0.37). The storage modulus at 1 Hz E′ changed by the degree of swelling Q satisfying with a power low as E′ ∼ Q−3.8. Microphotographs of the gels in a dry state showed that PVA network developed extensively as increasing the SS concentration. These results obtained strongly indicate that the resultant gel consists from only PVA, not composites of PVA and SS. It can be considered that SS hastens the aggregation or crosslinking of PVA chains; as a result physically crosslinked gels with close network and high elasticity were obtained. Reswelling experiment showed that the degree of swelling by the reswelling for the resultant gel was approximately 10, which was less than 1/6 of the original value of the degree of swelling.