Viscoelasticity and Rheological Hysteresis

TL;DR

This paper investigates the hysteresis behavior of complex fluids under cyclic shear-rate sweeps using the Giesekus model, revealing that viscoelastic materials can exhibit hysteresis features similar to thixotropic ones, cautioning against simplistic interpretations.

Contribution

The study demonstrates that viscoelastic materials can produce hysteresis loops similar to thixotropic materials, challenging assumptions about hysteresis as a sole indicator of thixotropy.

Findings

Hysteresis loops in viscoelastic materials can resemble those in thixotropic materials.

The hysteresis loop area varies with sweep rate, showing bell-shaped curves.

Viscoelastic hysteresis may not be related to shear banding instability.

Abstract

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 ualitatively 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.