(318i) The Medium Amplitude Oscillatory Shear (MAOS) of Semi-Dilute Colloid Dispersions - Third Harmonic of the Suspension Stress

We study the response of semi-dilute colloidal dispersions under Medium Amplitude Oscillatory Shear (MAOS). Using an excluded annulus model of the hard-core repulsion and hydrodynamic in- teractions among the particles, we determine the third harmonic of the stress response of a colloidal dispersion in the pair limit. Importantly, the influence of hydrodynamic forces, both in magnitude and in character, on the MAOS of semi-dilute dispersions is made explicit through comparison of such nonlinear rheological properties while varying the ratio of the hard-core to hydrodynamic radius. We show through comparison with experiments that hydrodynamic forces have a considerable effect on the microstructure of dispersions undergoing MAOS. Consequently, the nonlinear, oscillatory rheology of semi-dilute suspensions is quite sensitive to non-conservative, hydrodynamic, forces.