抄録
Development of shearing stress after the onset of simple shearing flow of two thixotropic solutions of polyvinylchloride in dibutylphthalate was measured at various rates of shear with a Weissenberg rheogoniometer. The sample solution was sheared at a rate of shear γ0 until steady-state stress was reached, and subsequently left to stand still for a length of time t0. Then rate of shear was changed to a new value γ and transient shearing stress was measured. This procedure was repeated for different combinations of γ0, γ and t0. When γ0<γ, stress overshoot appeared even for vanishingly small t0, and the maximum stress increased with increasing t0 over the range of t0 greater than one month. When γ0>γ. stress overshoot appeared only for t0 greater than a few days. In this case, increase of stress overshoot with t0 was small as compared with the case γ0<γ. These results were discussed from the view point of formation of structure in the solution during to and destruction under shear. Finally, effect of t0 on stress overshoot was compared with the theoretical calculations based on the Bogue model for non-linear viscoelasticity
