A kinetic theory for polymer melts. V. Experimental comparisons for shear-flow rheological properties

The steady-state and unsteady-state rheological properties calculated from the Curtiss–Bird kinetic theory are compared with experimental data on polymer melts and concentrated polymer solutions. It is found that the experimental curves for viscosity and primary normal stress differences vs shear rate for some liquids have very nearly the same shapes as the theoretical curves with the link tension coefficient ε in the range 0.3 to 0.5. For sudden startup of steady shear flow at t=0, the theory correctly predicts the observed stress overshoot for both shear and normal stresses; the theory predicts a sudden jump in the shear stress at t=0, this apparently unrealistic behavior being related to the stiffness of the links in the chain model. The complex viscosity in small-amplitude oscillatory motion does not agree with the experimental data in the high-frequency range, but at low frequencies the empirical Cox–Merz rule is followed approximately.