Microstructural response of dilute colloidal gels to nonlinear shear deformation

The time-resolved microstructural response of dilute, depletion-induced colloidal gels prepared in a density and refractive index matched solvent, to nonlinear shear deformation was investigated in 3D by fast scanning confocal microscopy in a custom-built cone-and-plate shear cell. Two sets of experiments were performed by manipulating the connectivity of the gel network with the stationary plate, thereby changing the flow boundary conditions. The gel structure evolves from its quiescent state via local rearrangement, rupture, and densification, first to a highly anisotropic network oriented near the extensional component of the shear flow field, and eventually to a mixture comprised of dense clusters and large voids. The transitions between these stages are highly sensitive to the boundary condition at the stationary plate. Our findings indirectly support the notion of soft pivot points along the backbone of dilute colloidal gels with centrosymmetric interactions, and will have important implications for the nonlinear rheology of colloidal gels and other structured fluids.