Developing a Thermodynamically consistent Constitutive Equation for Thixotropic fluids

Thixotropy is a ubiquitous property exhibited by typical consumer and food products like toothpaste, ketchup as well as materials of industrial value like drilling muds, cement, paints, and coatings [1]. The primary characteristic of such materials is the time-dependent rheology, as their viscosity decreases upon agitation but increases again over time when the fluid is allowed to relax. This behavior is a consequence of complex microstructures and has a dependence on the flow and shear history of the material as well. Several attempts have been made to understand the flow behavior of such fluids quantitatively, but none of the models in existence fully captures the complexity that arises due to the microstructure for any arbitrary flow [2]. Since only phenomenological models exist for the length scales relevant to the industries, a general model would not only widen our understanding, but also aid in improving the material processing, and potentially enhance the products.

The primary aim of this research is to take a step toward a truly predictive, rigorous, tensorial framework which will capture the details arising at the microstructure level in a thermodynamically consistent fashion. Coarse-grained population balance models have been shown to accurately capture the flow of thixotropic colloidal suspensions with yield stress [3]. This research aims to combine continuum nonequilibrium thermodynamics (NET) framework and population balance model derived from particle properties to formulate a constitutive model robust enough to predict fluid flow at larger length and time scales, with parameters grounded in physical quantities.

References

[1] J. Mewis and N. J. Wagner, “Thixotropy,” Adv. Colloid Interface Sci., vol. 147–148, pp. 214–227, 2009.

[2] R. G. Larson, “Constitutive equations for thixotropic fluids,” J. Rheol. (N. Y. N. Y)., vol. 59, no. 3, pp. 595–611, 2015.

[3] P. M. Mwasame, “Multiscale modeling of fundamental rheological phenomena in particulate suspensions based on flow-microstructure interactions,” University of Delaware, 2017.

Publications