Modeling the Complex Rheology of Charged Colloidal Suspensions

Colloidal suspensions are used in a variety of industries ranging from cosmetics to pharmaceuticals, where product viability often relies on its stability and flow behavior. Although the relationship between suspension composition and rheological behavior is crucial for product development, it is not fully understood, particularly regarding the effect of charged species on suspension properties. The addition of ions is a common practice in many formulations, and can have unpredictable effects on product performance, complicating efforts to design stable and effective suspensions. This project aims to bridge this gap by developing a model on the effect of ion concentration on the rheology of charged colloidal suspensions. This model was made using LAMMPS simulation software, utilizing the Yukawa potential to model silica dioxide microspheres in suspension. The charge of the simulated matrix is characterized by the Yukawa potential’s corresponding Kappa value. Our model showed that increasing the ion concentration in the matrix shifts the rheology from a shear thinning behavior to a Newtonian behavior. This model was confirmed experimentally using a 0.40 volume fraction of 7.75 µm silica dioxide microspheres suspended in ethylene glycol, using potassium chloride (KCl) as the ion additive. The experimental data aligned closely with the model, showing the same rheological shift as ion concentration increased. Future work will involve small-angle neutron scattering to obtain information about the interaction potential, helping us understand the relationship between structure and viscosity.