| Polyvinyl alcohol (PVA) hydrogels were prepared using aqueous PVA solutions containing various dimethyl sulfoxide (DMSO) concentrations. Remarkably different PVA hydrogels were obtained by varying processing parameters, i.e. DMSO concentration, initial PVA concentration and quench temperature. A large variation in the surface and bulk structures of PVA hydrogels was observed by scanning electron microscopy for samples prepared by freeze-etching and critical point drying techniques.;The processing conditions have a dramatic effect on the physical and mechanical properties of PVA hydrogels. PVA hydrogels prepared at low quench temperature using moderate to high DMSO concentrations have a low water content and a significantly improved hardness, tensile strength, elongation and tear resistance. Maximum properties are typically obtained near 75 wt% DMSO and at ;By varying the processing parameters, the gelation mechanism is altered which leads to three different types of hydrogel structures: (1) homogeneous gel, (2) heterogeneous gel without orientation, and (3) heterogeneous gel with oriented domains. Structural models representing the three types of hydrogels are proposed.;The swelling behavior of PVA hydrogels in aqueous solutions of organic salts was investigated. The reswelling behavior of hydrogels was also studied using dehydrated specimens. Attempts were made to characterize the crystallinity of PVA hydrogels using a differential scanning calorimeter. The viscoelastic behavior of hydrogels was studied using a dynamic mechanical analyzer. |
