Microstructure in sheared non-Brownian concentrated suspensions

The shear-induced microstructure in non-Brownian suspensions is studied. The Pair Distribution Function in the shear plane is experimentally determined for particle volume fractions ranging from 0.05 to 0.56. Transparent suspensions made of PMMA particles (172μm in diameter) dispersed in a fluorescent index matched Newtonian liquid is sheared in a wide gap Couette rheometer. A thin laser sheet lights the shear plane. The particle positions are recorded and the pair distribution function (PDF) in the shear plane is computed. The PDF at contact is shown to be anisotropic, with a depleted area in the receding side of the reference particle. The angular position of the depleted zone, close to the velocity axis at low particle concentration, is tilted toward the dilatation axis as the volume fraction is increased. At high concentrations (larger than 0.45), the shape of the PDF changes qualitatively with a secondary depleted area in the compressional quadrant of the main flow and a probability peak in the velocity direction. These experimental results are in good agreement with numerical simulations in Stokesian Dynamics where the interaction force between particles has been tuned to reproduce the particle roughness effects.