Modeling the non-Newtonian rheology of suspensions containing dissolved polymers

Suspension rheology exhibits a wide range of non-Newtonian behavior such as shear-thinning, shear-thickening and yield stress development. The rheology is dependent on solids concentration, colloidal and hydrodynamic forces. However, the mechanisms responsible for the complex rheology are not well understood.; A modified Stokesian dynamics technique is proposed to model suspension rheology. Three different mechanisms for shear-thinning are described and quantified. The prediction of shear-thinning due to Brownian motion compares well with experimental data; low and high shear rates give random and layered structures, respectively. Shear-thinning for repulsive forces between particles is caused by the breakup of an ordered or semi-crystalline configuration as the shear rate increases. For suspensions flocculated into a secondary minimum, shear-thinning is produced by breakup of particle aggregates as the hydrodynamic forces dominate the interparticle forces. The model predicts that boundary interactions influence the viscosity predictions. Smooth walls cause slip planes to form that reduce suspension viscosity. Rough walls disrupt slip plane formation and cause an increase in the low shear rate viscosity predictions. The development of a yield stress behavior is predicted when the boundaries are considered rough. Model predictions compare well with past experiments.; The model was modified to include the influence of a viscous, shear-thinning fluid phase. Correction factors are reported to describe a range of shear-thinning fluids. The model predictions are compared with data from the literature.; Model predictions are compared with viscosity measurements of mixtures of a monodisperse polystyrene latex and carboxymethyl cellulose (CMC). Low and high molecular weight samples of CMC are used. Increasing CMC concentration causes the rheology to change from Newtonian to shear-thinning. The model predicts the degree of shear-thinning behavior assuming a depletion attraction mechanism. The higher molecular weight CMC decreases the shear rate for the onset of shear-thinning and reduces the relative viscosity compared to the lower molecular weight CMC.