OSMOTIC AND SCATTERING PROPERTIES OF CHEMICALLY CROSS-LINKED POLY(VINYL ALCOHOL) HYDROGELS

Swelling pressure and shear modulus measurements are reported for chemically cross-linked poly(vinyl alcohol) (PVA) hydrogels. An attempt is made to correlate the macroscopic results with data obtained by small-angle X-ray scattering (SAXS) measurements performed on the same gel samples. The swelling pressure of the PVA gels can be satisfactorily described by a two-term equation consisting of a separable elastic and mixing contribution. The concentration dependence of the elastic term differs slightly from the classical theoretical prediction. The mixing term follows a power law behavior with an exponent close to that predicted by scaling theory. Osmotic pressure results obtained for aqueous PVA solutions are used to normalize the SAXS spectra to yield absolute scattering intensities. The scattering spectra of the gels are resolved into a static and a dynamic (solution-like) component. The intensity of the latter is compared with values calculated from independent osmotic measurements. The second moments describing the static concentration fluctuations are found to increase strongly with the cross-linking density.