(108c) Rheology and Microstructural Development in Oscillating Suspensions of Non-Colloidal Spheres

Rheological measurements are used to assess the existence and rate of microstructural changes in oscillating suspensions of non-colloidal spheres. Though slightly non-linear, naively separating the stress response into components in and out-of-phase with the strain reveals that the two components change at different rates. Rapid and large changes in the storage modulus occur over the first 15-20 oscillations for concentrated suspensions in the vicinity of a strain amplitude of one. The loss modulus is much larger than the storage modulus and appears to remain constant over the first twenty oscillations. However, the loss modulus does change slowly, consequently requiring large numbers of oscillations to reach steady state. The results are qualitatively independent of the shear cell geometry, suggesting that shear-induced particle migration is unimportant and that the observed behavior results from changes in the suspension microstructure. Comparison of the experimental results at small total strains to simulation results provides insight into the rapid changes of the storage modulus. Extending the range of volume fractions and total strains beyond previous investigations, as well as a more detailed study of the response at small total strain, has provided a more comprehensive view of the rheology.