Swelling and mechanical properties of poly(vinyl alcohol) hydrogels

Poly(vinyl alcohol) (PVA) aqueous solutions (of high water content) were repeatedly frozen and thawed to obtain PVA hydrogels. Both the degree of cross-linking and the viscoelastic behavior of the network structure in the PVA hydrogels varied directly as a function of the number of freeze-thaw cycles, as well as the thawing temperature. Swelling kinetics of these PVA hydrogels in water were studied by weighing hydrogels swollen with water at various temperatures and time points. The rate of swelling of PVA hydrogels linearly increased with the square root of immersion time in water. A comparison of the amount of water in the swollen PVA matrix with the variation in the storage modulus of PVA hydrogels demonstrated a tendency for decrease in water absorption, as well as an increase in elasticity, with increasing cross-link density and network structure formation in these PVA hydrogels. The rate coefficients of swelling, defined as the change in the absorbed amount of water in the hydrogel vs. the square root of immersion time, increased with increasing temperature of the swelling procedure.