(30h) Rheo-Electric Investigation of Carbon Black Suspensions Undergoing Shear-Induced Microstructural Rearrangement

Carbon black is ubiquitous as a conductive additive in electrochemically active slurries for emergent energy storage and capacitive desalination systems. When suspended, these high-structured, electrically conductive particles agglomerate, creating a charge-carrying microstructure that facilitates electron transport. In our initial work, we surface oxidized carbon black particles and enhanced their colloidal stability. We showed that reduced agglomeration led to a decrease in the electronic conductivities of the particles in deionized water. This demonstrated a non-trivial connection between the carbon black microstructure and its electrical response. This microstructure additionally evolves under flow, leading to a varied electrical response depending on the suspending medium and the flow conditions. To further investigate this varied response, we dispersed neat carbon black particles in Newtonian fluids with varying dielectric constants and viscosities. The formulated carbon black suspensions also spanned a range of volume fractions above the electrical and mechanical percolation thresholds for each solvent. We sheared the suspensions from 2500 to 10 s^-1 and characterized the microstructural rearrangement of the agglomerates by calculating the Mason number. At each flow regime, we performed in situ impedance frequency sweeps on the suspensions and obtained their conductivities, relative permittivity, and dielectric strengths by fitting the dielectric spectra to several models. By parametrically pairing the measured mechanical and dielectric properties, we reveal the systematic dependence of the mechanism of charge transport on not only the microstructure of the carbon black agglomerates but also the solvent properties. We believe that this qualitative insight will provide crucial design rules towards the development of slurries with optimal performance.