Yield stress and wall slip of kaolinite networks

Abstract

In this work, the nonlinear rheological properties of kaolinite suspensions as a model fluid were studied. Three kaolinites with different average particle, aspect ratio and asperity were used to gain a deeper understanding of the effects of particle's geometry on yielding, rheology, and apparent slip velocity over a wide range of concentrations in the semi-concentrated to concentrated regime. To reveal the impact of geometry on kaolinite suspension's rheology, atomic force microscopy was employed, thus revealing unique information about the particle's structural differences. The apparent slip velocity was studied through the application of the Mooney technique using experimental data from parallel-plate geometry at various gap spacings. Sandpaper of varying grit was used to eliminate slip and estimate the true rheological parameters including the yield stress of these materials. Kaolinite suspensions were found to follow a Herschel-Bulkley model with yield stress that increases with concentration irrespective of the type of kaolinite particles. The aspect ratio and asperity of particles were found to alter their slip behavior by enabling the kaolinite network to have a tunable yield stress. It was also determined that the existence of resilient larger clusters at higher shear rates often induce higher slip effects.