THERMODYNAMIC PROPERTIES OF POLY(VINYL ALCOHOL) AND POLY(VINYL ALCOHOL VINYL-ACETATE) HYDROGELS

Osmotic and light scattering observations are reported for chemically cross-linked poly(vinyl alcohol) and poly(vinyl alcohol-vinyl acetate) hydrogels and the corresponding semidilute polymer solutions. The osmotic contribution of the network polymer is obtained from swelling pressure and shear modulus measurements. The free energy of mixing in the cross-linked polymer is found to be significantly smaller than that of the polymer solution at the same concentration. Small-angle neutron scattering and static light scattering measurements indicate the presence of large-scale static structures in the systems. The fluctuating part of the total scattered intensity determined from simultaneous dynamic and static light scattering measurements is compared with the results of macroscopic osmotic observations. Reasonable agreement is found between the results of the two entirely different experiments.