Rheology of suspensions of cubic particles

The rheology of non-Brownian suspensions containing nonspherical particles, such as cubes, remains largely unexplored, despite their relevance in both industrial and natural contexts. While many studies have focused on suspensions of spherical particles, only a few have investigated the viscosity of suspensions with cubiclike particles, and none have quantified the particle normal stresses in such systems. In this work, cubic particles were fabricated using a soft lithography technique and suspended in a Newtonian fluid. Rheometric experiments were conducted to determine the Einstein and Batchelor coefficients in the dilute and semidilute regimes, revealing stronger hydrodynamic interactions compared to spheres. In the concentrated regime, viscosity measurements as a function of shear stress exhibit shear-thinning behavior, which can be effectively captured by introducing a shear-dependent jamming volume fraction. The viscosity is significantly higher—or equivalently, the jamming fraction markedly lower—than in spherical particle suspensions. The third normal stress component (in the vorticity direction) is measured through resuspension experiments. We show that, for a given shear stress, the sediment spreads significantly more in suspensions of cubes than in suspensions of spheres, indicating substantially higher particle normal stresses than in the spherical case. Finally, at a given solid fraction, the ratio of the third particle normal stress to the shear stress is found to be of the same order for suspensions of spherical and cubic particles.