Observing the finite-rate dynamics of deformations in an amorphous material

In an amorphous solid, applied shear can cause localized reversible rearrangements of particles. At low strain rates, each rearrangement can be viewed as a discrete switching event, forming the basis of quasistatic models that explain the system's ability to remember amplitude(s) of oscillatory shear. However, this picture largely ignores the system's dynamics at finite strain rates, due to rearrangements' finite relaxation rates. We perform experiments on a monolayer of bidisperse colloidal particles stabilized at a level decane-water interface. A series of strain protocols are used to form and read out memories while we observe the trajectories of particles. We study how the heterogeneity in rearrangements' timescales expands the set of states that can be reached by finite-amplitude shear. We consider whether these dynamics give the system a readable memory of strain rate.