Strain Driven Ordering of Nanoparticles in a Dense Silica Colloid

 In a dense monodisperse hard sphere colloid, ordering and disordering of particles can occur driven by an oscillatory shear of the system.  This transition is purely controlled by strain amplitude, different from the normal shear thickening behavior that occurs at a much higher critical shear stress. Using in situ Rheo-SAXS setup, we measured simultaneously the rheological response and the structural evolution of a silica colloid under different shear strain amplitudes. We reveal that, under different strains, there is a different time-dependent ordering kinetics towards a dynamic equilibrium with different degree of ordering.  When the strain amplitude reaches a critical value that starts to induce disordering in the system, the pathway towards the dynamic equilibrium can also become highly non-monotonic.  Within each oscillatory cycle, there is a strong correlation of ordering with different phase of the oscillation, indicating reversing the shear direction could disrupt some ordered region locally.