(654e) Rheological and Electrical Percolation Behavior of Carbon Black Suspensions in Polar Aprotic Solvents

In this work, the microstructural origin of the rheo-electric behavior of carbon black gels and suspensions is studied. These materials find widespread use as conductive fillers in composites and slurry-based electrochemical energy storage technologies. In these applications, both the viscosity and electrical conductivity are key design parameters and are determined by the microstructure. Using small angle neutron scattering (SANS) and electron microscopy, we perform detailed structural analysis on carbon black suspensions as a function of volume fraction for two commonly used conductive additives – KetjenBlack and Vulcan. From these measurements, the static structure factor is determined and characterized at low-Q by a power-law scaling I(Q) ~ Q^-3. We characterize the onset of gelation using oscillatory rheological measurements and identify the percolation threshold associated with the jamming transition. While the onset of mechanical percolation is commonly associated with the electrical percolation threshold for these materials, results from impedance spectroscopy measurements show that the electrical percolation threshold occurs at far lower volume fractions. Further, analysis of the critical scaling parameters associated with the rheology are inconsistent with those extracted from the conductivity. These results suggest a rich relationship between electrical conductivity and the fluid properties of carbon black dispersions that could guide the design of future low-viscosity, high conductivity conductive additives for electrochemical flow applications.