Rheology and structure of poly(vinyl alcohol)-poly(ethylene glycol) blends during aging

Abstract

We have used rheometry and dynamic light scattering to study the evolution of the properties of concentrated aqueous solutions of poly(vinyl alcohol) (PVA) and blends of PVA and poly(ethylene glycol) (PEG) as they age. We find that freshly prepared materials are primarily viscous, though they shear thin at low-shear rates and show signs of shear-induced structure at higher shear rates. The viscosity of pure PVA solutions increases slowly as they age. The aging of the PVA/PEG blends is much faster, however, and for sufficiently high concentrations of PEG, the blends gel over the 1-month time scale of our observations. Dynamic light scattering experiments show the presence of two relaxation processes in both the pure PVA solution and the blends, with relaxation times that depend on the polymer concentration and the aging time. Both the rheological and dynamic light scattering measurements show the existence of microphase separation in the blends and suggest that the presence of PEG forces the PVA solution to phase separate and eventually to gel. However, we find that the gel transition is not sharp, with different signatures of gelation occurring at different times, depending on the length scale at which the gel is probed.