Direct Visualization of Shear in a Colloidal Glass

A real-space, 3-D observation of the shear process in a glass, using a model hard sphere colloidal glass, visualized with confocal microscopy. The figure is a reconstruction of the particle motions in a 20 µm by 20 µm by 15 µm volume of an amorphous colloidal suspension as the suspension is sheared. The suspension is composed of 1.5 µm monodisperse hard-sphere silica particles. The motions of the individual particles are tracked using confocal microscopy. The results allow Spaepen and Weitz to identify the local shear rearrangement, or "flow defect," that governs the flow rate, the number of atoms involved and the strain upon rearrangement. The use of a model hard-sphere colloid system increases the length scale, allowing processes that are normally at the atomic scale to be visualized at the optical scale.