(458e) Direct Visualization of Strain-Induced Yielding In Colloidal Gels

Colloidal gels are space-spanning networks of particles formed due to strong interparticle attractions. They yield when a critical strain is applied, resulting in fluidization and bond rupture. Colloidal gels are common to many industries, including consumer products, pharmaceuticals, and chemical processes. The connection between the viscoelastic behavior of gels and their arrested structure is well-documented, but there is uncertainty as to the mechanism and causation of gel yielding, especially in the case of high strain-rate deformation typical of industrial processes and transportation. We directly visualized, using a confocal laser scanning microscope, the local microstructural evolution in depletion gels before and after yielding at large strains and during structural recovery. We used UV photopolymerization to immobilize the gel structure at various stages of flow and relaxation. We quantified the short- and long-range structure of these gels using structural parameters such as contact number distributions and number density fluctuations. In addition, we independently examined the rheology of yielding and recovery with oscillatory shear and creep experiments, with the aim of drawing a connection between structural changes and macroscopic rheological phenomena.