Hard sphere glasses under oscillatory shear (The final Episode?)

The latest rather than final episode of the "SHEARING HARD SPHERE GLASSES" production will be presented. We investigate particle rearrangements in colloidal glasses subjected to oscillatory shear strain by the technique of Light Scattering Echo (LS Echo). LS Echo directly follows the motion of the particles through peaks (echoes) in the intensity autocorrelation function; the height of the peak measures the elastic rearrangements in the sample. Polydisperse hard sphere PMMA particles were used to avoid crystallization under shear. The yielding behaviour is monitored through the irreversible particle rearrangements for different volume fractions in the glass phase region. Decreasing the volume fraction glasses are found to yield at strains as high as 20\% while the irreversible rearrangements are progressing more gradually with strain for low fraction glasses. The behaviour of large order echoes at long times is related with effects of shear on the frozen-in fluctuations of the glass. Monodisperse spheres on the other hand do crystallize under shear complicating their yielding behaviour. Some rheological measurements providing complementary information will also be presented. The notion of elasticity and reversibility of glasses under oscillatory shear may be discussed. Jamming might also play a role...