Dynamics of shear-induced yielding and flow in dilute colloidal gels

The transient microstructural response of dilute, depletion-induced colloidal gels to shear deformation is probed using a custom-built cone-and-plate shear cell mounted on a fast scanning confocal microscope. We directly unveil an important mode of nonlinear gel yielding, which marks the transition from an immobilized gel network to disconnected flowing clusters at large values of the accumulated strain (γ ~ 0.7). The transition is mediated by a cascade of local rupture events that initiate at the sample's outer edges and propagate inward, resulting in transient dynamic and microstructural heterogeneities in the gel network. Based on the findings, we propose solvent-induced drag as the primary cause of nonlinear rupture, and discuss the coupling between the microstructural evolution and transient rheology in this system.