Rheological Characterization of the Gelation Behavior of PVA Solutions in DMSO Containing BA

Abstract

The gelation behavior of poly(vinyl alcohol) (PVA) solutions in dimethyl sulfoxide (DMSO) containing boric acid (BA, H3BO3) under shear stress was rheologically investigated in terms of temperature and molecular weight of PVA. Time-dependent rheological properties of the solutions were analyzed to determine the effects of stress on the gelation mechanism. The solutions of low weight-average molecular weight (Mw=31,000−50,000) PVA showed more noticeable temperature-dependent viscosity changes than those of high weight-average molecular weight (Mw=165,000−186,000) PVA. The viscosity increase caused by stress indicated that the formation of the gel structure was promoted by stress.In time sweep experiments, all the PVA solutions showed stress-dependent rheological responses except for the high Mw PVA solutions at 30 oC. The viscosities of the solutions remained constant over the observed shearing time, indicating the formation of an irreversible gel. The effects of stress history were reconfirmed by the results of frequency sweep experiments. Antecedent shearing gave rise to many different time-dependent rheological responses. At 60 oC, both low and high Mw PVA solutions had loss tangent values (tan δ) less than 1. Furthermore, the formation of gel structures increased the relaxation time (λ) by up to 10 s.