Direct Investigation of 3D Suspension Microstructural Evolution

Knowing the microstructure formation in sheared suspensions is key to understanding the rheological behavior of such systems.  Stokesian dynamics simulations (e.g., Foss and Brady, J. Fluid Mech., 2000) predict anisotropies as a result of multibody hydrodynamic interactions.  Thus far, few systems have elucidated data that can be directly compared to theory and computation. To determine the microstructure of near-hard-sphere microparticle suspensions, the local pair distribution function is presented based on experimentally obtained 3D particle positions using dynamic confocal laser scanning microscopy of fluids subjected to pressure-driven flow across various local volume fractions and shear rates. Evolution of structure from and isotropic distribution to that formed as a result of shear is elucidated.  Silica suspensions of various pH values and electrolyte concentrations are investigated out of an interest on the competition between hydrodynamic and electrostatic forces. The results capture the evolution of suspension microstructure as a result of this competition. Explanation for this transition and its implication on suspension rheology is discussed.