Special Features of Nonlinear Behavior of a Polymer Solution on Large Periodic Deformations

Study of the behavior of polymer solution flows in the region of nonlinear viscoelasticity allows one to more accurately evaluate the adequacy of rheological models and to describe the rheological properties of a material in more detail. The nonlinear viscoelastic properties manifesting themselves in the process of studying the behavior of a polymer material on significant deformations were investigated with the aid of time dependences of shear stresses calculated at different amplitudes. The present work considers the applicability of the modified Vinogradov-Pokrovskii rheological model to describing the oscillating shearing of polymer fluids with a large amplitude. It has been established that on increase of the deformation amplitude, the shear stresses cease to be a true harmonic, and one observes the appearance of a "step" on their left front, which speaks of the substantial nonlinearity in the behavior of the sample. The obtained theoretical dependences are compared with experimental data for a 5% solution of polyethylene oxide in dimethyl sulfoxide. The comparison was made as by plotting the time dependences of normalized stresses, so by analyzing Lissajous figures. Despite the simplicity, the modifi ed Vinogradov-Pokrovskii rheological model adequately describes the behavior of polymer materials on significant periodic deformations.