Characterizing Individual Shear Defects in Colloidal Glasses*

Although the mechanisms governing plastic deformation in crystals have been well-understood for decades, we lack an equivalent depth of understanding for amorphous materials. Colloidal glass provides a unique experimental system with which to study the structure, defects, and dynamics of a generic amorphous material. We analyze particle-level trajectories and local strain fields obtained from experiments on ~1-μm-diameter, hard-sphere colloidal glasses under conditions of uniform shear. We directly identify individual “shear defects” or “shear transformation zones” (STZs) as they are activated in the glass, by cross-correlating the measured local strain field with that predicted for Eshelby inclusions. By fitting for both the STZ location and size, it is possible to identify the specific particles that comprise an individual STZ and directly determine how their free volume, local density, coordination, and other structural predictors evolve leading up to and after the shear transformation.