Gelation behavior of the solutions of poly(vinyl alcohol) (PVA), whose syndiotactic diad content was 52% and weight-average molecular weight of PVA ranged from 89,000 to 186,000, in dimethyl sulfoxide (DMSO) was investigated in terms of shear rate, concentration, and molecular weight of the polymer. To trace time-dependent gelation behavior, a programmed time sweep experiment was carried out by repeating the following procedure 3 times; 10 min of measurement followed by 5 min relaxation. All of the PVA solutions in DMSO exhibited time-dependent rheological responses, particularly under low shear rate of 2 rad/s, indicative of the formation of physical structures. At high shear rate of 200 rad/s the rheological responses were independent of time. Referring to Winter's view on gelation, a weak shear produced a soft gel structure whereas a strong shear produced an irreversible strong gel. Gelation was more affected by molecular weight than by concentration over the period of shearing. At low frequency, relaxation time was increased with time, and then leveled off after prolonged shearing. At high frequency, however, little change of relaxation time was noticed. They can be interpreted as a consequence of formation of three-dimensional gel structure through the polar interactions by hydroxyl groups whose strength was dependent on shearing conditions.
- Shear-induced structural formation
- Solution rheology