POLY(VINYL ALCOHOL VINYL-ACETATE) COPOLYMER HYDROGELS - SCATTERING AND OSMOTIC OBSERVATIONS

Light and small angle X-ray scattering measurements have been made on chemically cross-linked poly(vinyl alcohol-vinylacetate) copolymer hydrogels and on the corresponding semidilute solutions. The results of these observations are compared with elastic and osmotic measurements performed on the same networks. The variation of the intensity of the dynamic component of the scattered light was investigated as a function of the cross-linking density. At low cross-linking density, the observed intensity arising from concentration fluctuations in the gel exceeds that of the corresponding solution, while at higher cross-linking density the opposite is true. In the solution, the intensity correlation function exhibits two well-separated relaxation processes, both of which are diffusive; i.e. the relaxation rates vary as Q2. The fast relaxation process describes the cooperative motions of the polymer in the solvent.