Dynamic Shear Rheology of Thixotropic Suspensions: Comparison of Structure-Based Models with Large Amplitude Oscillatory Shear Experiments

Rheological measurements on a model thixotropic suspension developed by Dullaert and Mewis are performed, including large amplitude oscillatory shear (LAOS) flow, shear flow reversal, and a novel unidirectional LAOS flow, to provide an extended rheological data set for testing constitutive models. A new structure-based model is developed by improving the elastic stress component in the Delaware thixotropic model. Model parameters are determined from steady, small amplitude oscillatory and step shear rate tests, and the model predictions are tested against LAOS experiments. Similar comparisons are made for three other literature models: two of which use a scalar internal structural parameter and include the modified Jeffrey’s model proposed by De Souza and Thompson, while the third model developed by Bautista et al. is based on fluidity additivity. A common weakness in all models is identified to be the use of scalar order parameters that cannot account for the reversal of flow directionality inherent in LAOS flow. This is further illustrated by comparison of the models in flow reversals and by contrasting with predictions obtained in a novel unidirectional LAOS experiment where flow reversal does not take place.