Viscoelasticity and rheological hysteresis

Rheological characterization of complex fluids subjected to cyclic shear-rate sweep often exhibits hysteresis. Since both viscoelastic and thixotropic materials show hysteresis loops, it is important to understand distinguishing features (if any) in the same shown by either. Lately, there has been substantial work that attempts to relate the area enclosed by the hysteresis loop with the manner in which shear rate is varied in the cycle, in order to infer thixotropic parameters of a material. In this work, we use the nonlinear Giesekus model to study its response to the application of cyclic shear-rate sweep. We find that this model produces each type of qualitatively similar hysteresis loop that has hitherto been ascribed to thixotropic materials. We also show that the area of the hysteresis loop for a viscoelastic material as a function of sweep rate shows bell-shaped/bi-modal curves as has been observed for thixotropic materials. This study illustrates that caution needs to be exercised while attributing hysteresis loops and associated features observed in a material exclusively to thixotropy. Another feature related to the hysteresis loop is the occurrence of shear banding instability. We find that viscoelastic hysteresis may not have any connection to shear banding instability.

Automated summary

In this study, the nonlinear Giesekus model was used to investigate the response of cyclic shear-rate sweep. The research found that this model produces hysteresis loops similar to those observed in thixotropic materials. Additionally, it was shown that the area of the hysteresis loop for viscoelastic materials exhibits bell-shaped/bi-modal curves similar to thixotropic materials. The study suggests caution is needed when attributing hysteresis loops and associated features solely to thixotropy, and that viscoelastic hysteresis may not be connected to shear banding instability.