(513f) Structural Breakdown in Sheared Carbon Black Suspensions

The behavior of colloidal suspensions under applied deformation is an important factor in the design of a variety of materials ranging from foodstuffs and personal care products to cements and battery electrodes. Many studies have shown that the properties of these suspensions are directly related to the material microstructure, which is subject to change under flow. While much progress has been made to understand the effect of flow on the microstructure of stable colloidal suspensions, less well understood is the behavior of suspensions of particles with non-uniform shapes and strong attractions, especially at relatively high particle loadings. In this work, the shear-induced microstructure of a series of carbon black suspensions exhibiting strongly attractive interactions is directly measured at a range of applied shear rates by performing Rheo-USANS (Ultra-Small Angle Neutron Scattering) experiments at the NIST Center for Neutron Research. These experiments shed light on the combined effect of interaction strength and particle loading on the shear-dependent size and fractal dimension of carbon black agglomerates. Furthermore, the relationship between the shear-dependent microstructural, electrical, and rheological properties of these suspensions is explored by performing complementary rheo-dielectric measurements under similar conditions. These experiments confirm that the shear-thinning behavior commonly observed in these suspensions arises due to the erosion of carbon black agglomerates with increasing shear rate. Additionally, the effect of shear is also observed in the electrical behavior where upon yielding, a system-spanning network of inter-agglomerate bonds is broken and a consequent decrease in electrical conductivity is observed. The extent of the shear-dependence of these macroscopic properties is also shown to depend on the relationship between applied shear and the microstructure of the suspension. This work has implications for understanding and predicting the behavior of colloidal suspensions under shear as well as for the design and end use of colloidal suspensions for many applications.