Understanding the relationship between plasticity and material microstructure in disordered systems

How soft, disordered materials yield is a question of fundamental interest to material engineers and physicists alike. In this talk, we explore~the relationship between the plastic flow-induced dynamics and microscopic structure of disordered colloidal solids. Our experimental setup~consists of~a~custom-built interfacial stress rheometer, in which a dense monolayer of repulsive colloidal particles~is placed and~undergoes cyclic shear. This~apparatus permits~simultaneous measurement of the material bulk rheology ($G'$,~$G'')$~and dynamic structure factor from particle trajectories, as well as~characterization of the suspension microstructure. We~quantify system-wide~structure using the concept of (structural) excess entropy, the difference between~system~entropy and that of an ideal gas.~The experiments reveal~that structural relaxation induced by plastic flow depends on and scales~with the strain-rate and microscopic order measured at earlier and later times, respectively. Thus, measurement of sample~\textit{static}~structure (excess entropy) provides insight about both strain-rate and constituent rearrangement~\textit{dynamics}~in the sample at earlier times. Moreover,~the relaxation times scale~with shear rate according to a classic shear thinning relation.