Rheology and Shear-Induced Structural Evolution in Model Conductive Carbon Black Suspensions

Carbon black is commonly used in many technological applications ranging from tire rubbers and inks to electrochemical energy storage devices. In these applications, shear plays an important role in determining end performance due to the shear-induced structural changes and resulting change in properties that occur during mixing, processing, and application steps. To understand this shear-dependent behavior, the microstructure of carbon black suspensions is directly measured by performing Rheo-USANS (Ultra-Small Angle Neutron Scattering) experiments at a range of applied shear rates for suspensions with varying interaction strength, particle loading, and building block characteristics. These experiments show that a dramatic structural transformation from large, dense agglomerates to small, open agglomerates is predictable using the inverse Bingham number, which compares the measured stress to the yield stress of the suspension. Additionally, at high shear rates, the self-similar breakdown of agglomerates is shown to be dependent on the Mason number, which compares shear forces to interparticle attractions. This structural evolution explains many behaviors that are not well understood such as apparent shear-thickening and tunability of yield stress and elasticity.