Traction Force Rheology: a new technique to understand the mechanics of colloidal solids

We present recent results on the structural and mechanical response of colloidal solids in response to externally imposed shear strain. We introduce a new technique, traction force rheology, that combines confocal and traction force microscopy. Using this technique, we simultaneously visualize the structural changes occurring within a colloidal solid during elastic and plastic deformation, and directly measure the mechanical response of the colloidal solid. We present stress-strain curves, measured in-situ, combined with full visualization of the mechanisms occurring within the colloidal solid at every point along the stress-strain curve. For colloidal polycrystals, these mechanisms include dislocation dynamics, grain boundary sliding, and grain refinement; for colloidal glass we visualize shear transformations. Experimental details, challenges, and current results will be discussed.