Surface property-driven nanoscale rheological behavior of kaolinite: a molecular dynamics study

Understanding the nanoscale rheological behavior exhibited by clay suspensions is crucial for the safety of engineering applications. However, experimental investigations at nanoscale are severely constrained by inherent limitations and the intricate interplay between clay surface properties and the intricate microstructure of these systems. This investigation utilizes molecular dynamics simulations to illuminate the fundamental rheological phenomena governing the behavior of kaolinite-water systems. The study focuses on exploring the impact of variations in kaolinite surface characteristics on rheological manifestations by employing parallel pore models incorporating diverse kaolinite surface configurations. Equilibrium molecular dynamics (EMD) and nonequilibrium molecular dynamics (NEMD) simulations were conducted to investigate the physical properties of kaolinite under zero shear conditions and various shear rates, respectively. The wettability of different surfaces of kaolinite leads to a regular distribution of water molecules, affecting the pore spacing after EMD equilibrium, resulting in differences in water molecule self-diffusion coefficient and viscosity, exhibiting a small pore effect. In the simulation, the interaction between two parallel kaolin particles was determined to weaken with increasing separation distance. Non equilibrium molecular dynamics (NEMD) simulations were used to analyze the migration of water molecules under shear in different pore types. The viscosity of water molecules is affected by shear rate and separation distance and decreases to varying degrees as they increase. Finally, the yield stress of kaolinite particles was calculated using the Bingham model. These findings provide important insights for evaluating the influence of different surfaces of kaolinite on its rheological properties and assessing the yield stress of kaolinite suspensions.