Stresses and particle dynamics in hard sphere crystals under oscillatory shear
George Petekidis (FORTH)
Complex Fluids: Suspensions, Emulsions, and Gels
Wed 10:45 - 12:15
Barus-Holley 160
The mechanical properties and the underlying particle dynamics of hard sphere colloidal crystals created by the application of oscillatory shear on a hard sphere glasses are studied by experiments and Brownian Dynamics simulations. Experimental rheometry reveals a drop of the elastic modulus upon a shear induced crystallization of a hard sphere glass. BD simulations show anisotropic particle rearrangements in the crystal in contrast to isotropic ones in the glass. Crystal displacements are due to cooperative motion of particle layers sliding over each other in the velocity-vorticity plane, thus exhibiting a yield strain less than that of the glass. Past the yield point, the longtime shear induced displacements of the glass are found to be larger, while stresses are highly correlated to instantaneous shear induced displacements. Thus during oscillatory shear of a monodisperse hard sphere particle glass, large out of cage displacements allow the system to explore the energy landscape and find the minima in energy, stresses and displacements by configuring particles into a crystal oriented parallel to shear. Experimentally the LS-Echo technique coupled with rheometry has been used to examine shear-induced particle rearrangements both in glasses and shear induced crystals. Although at low strains the crystal exhibits higher particle displacements than the glass due to relative larger local free volume (in-cage motion), at higher strains the crystal shows reduced particle rearrangements due to the anisotropic sliding layer motion. A qualitative comparison between the BD simulations on crystals and the experiments show good agreement at the high frequency regime, where a characteristic minimum of shear induced diffusivities as a function of frequency is observed.