| Abstract: | A stiffened and automated Weissenberg rheogoniometer has been used to measure time-dependent nonlinear properties of several polymer solutions in simple shear flow. Departures from finite linear viscoelasticity are correlated with molecular structure. It is shown that certain features of behavior at high shear rates can be explained if the Doi–Edwards equilibration process is taken into account. A method is outlined for calculating the characteristic time τe for this process as a function of concentration, molecular weight, temperature, and branch length. This characteristic equilibration time is incorporated into a simplified BKZ constitutive equation. The proposed equation is found to adequately describe a wide range of experimental results both in step-strain and continuous shear flows. |
