(356e) Modeling the Rheology of Aggregating Colloidal Suspensions: Insights from Population Balances and Non-Equilibrium Thermodynamics

Aggregating colloidal suspensions can be encountered in a large number of materials; examples include food products, biological fluids, printer inks, paints, and slurries. A consistent description of these suspensions remains challenging because their rheology directly connects to the mesoscale structure and aggregation kinetics. Transient flows in such suspensions exhibit complex dynamics due to yield stress, viscoelasticity, and flow history dependence, i.e., thixotropy. We developed a population balance-based constitutive model taking advantage of rigorously derived aggregation kernels for shear flow and Brownian motion and by using more physically based relations for rheology. The model captures the effect fractal agglomerates, observed in suspensions of fumed silica and carbon black, on the macroscopic rheological behavior by tracking their agglomerate size distribution during flow. The predictions show good agreement with a variety of rheology protocols, such as steady shear, step shear, and large amplitude oscillatory shear experiments. The agglomerate size predictions were validated against the simultaneous rheology and scattering measurements, Rheo-SALS and Rheo-USANS. A coarse-grained version of this model is also applied to describe rheological behavior of human blood which contains more complex rouleaux structures that form when red blood cells stack together at low shear rates.

Finally, we show that one can incorporate the principles of population balances in the framework of non-equilibrium thermodynamics such that the flow descriptions are generalizable to a three-dimensional system. We offer a top-down approach and show how the entropy associated with the agglomerate formation is related to the evolution equations of the distribution of aggregate sizes. Through a consistent tensor description from non-equilibrium thermodynamics, we also demonstrate how this modeling approach can capture phenomena such as inhomogeneities and stress-induced migration commonly observed in these systems.

Research Interests

I am interested in developing practical methods to predict physical behavior of materials using theoretical understandings gained from first-principles modeling. In my Ph.D. research, I developed constitutive models that combine the top-down (thermodynamics) and bottom-up (microstructure) information to gain understanding of aggregating suspension flows. Such hybrid frameworks can provide insights into structure-property relationships and emergent phenomena along with predictive capabilities using only a few adjustable parameters. Moreover, a theoretical foundation can pave the way for a systematic data-driven investigation, aiding the design of better experiments and discovery of new materials. The flexibility of these models also allows them to be paired with simulation techniques, such as computational fluid dynamics (CFD), in a computationally inexpensive manner.

Selected publications:

1. 1. Jariwala, S.; Wagner, N.J.; Beris, A.N. A Thermodynamically Consistent, Microscopically-Based, Model of the Rheology of Aggregating Particles Suspensions. Entropy 2022, 24, 717.
2. 2. Jariwala, S.; Horner, J. S.; Wagner, N. J.; Beris, A. N., Application of population balance-based thixotropic model to human blood. Journal of Non-Newtonian Fluid Mechanics 2020, 281, 104294.
3. 3. Beris, A. N.; Jariwala, S.; Wagner, N. J., Flux-based modeling of heat and mass transfer in multicomponent systems. Physics of Fluids 2022, 34, (3), 033113.
4. 4. Beris, A. N.; Horner, J. S.; Jariwala, S.; Armstrong, M. J.; Wagner, N. J., Recent advances in blood rheology: a review. Soft Matter 2021, 17, (47), 10591-10613.