Dynamics of the orientation behavior and its connection with rheology in sheared non-Brownian suspensions of anisotropic dicolloidal particles

The orientation, microstructure, and rheology in non-Brownian shear flow were studied for suspensions of dicolloidal particles using a novel particle mesh Ewald Stokesian dynamics algorithm for anisotropic particles. Four different particle shapes were studied with dicolloids modeled as the union of two intersecting spheres. Dynamic simulations were conducted for periodic systems of 1000 particles for volume fractions φ=0.05-0.55. The suspension microstructure was disordered for all particle shapes at 0 ≤ φ ≤ 0.50, with some systems showing ordered microstructure at φ=0.55. The viscosity in the disordered state was similar for all particle shapes at equal volume fraction. Negative first and second normal-stress differences were found for φ ≤ 0.5, but positive values were observed for certain ordered systems at φ=0.55. Complex orientation behavior was observed as a function of volume fraction and particle shape. All particles showed an orientation shift toward the vorticity axis for φ ≥ 0.10. Certain shapes showed a shift away from the vorticity axis for φ ≤ 0.10. The high φ orientation dynamics were consistent with predictions based on the mobility tensor M^ωS relating the angular velocity to particle stresslet. The orientation dynamics were dominated by the second normal-stress difference. The shift away from the vorticity axis for small φ was induced by migration away from orientations with large orientation fluctuations.