Evaluating the Rheo-electric Performance of Aqueous Suspensions of Oxidized Carbon Black

Hypothesis: The macroscopic properties of carbon black suspensions are primarily determined by the agglomerate microstructure built of primary aggregates. Conferring colloidal stability in aqueous carbon black suspensions should thus have a drastic impact on their viscosity and conductivity. Experiments: Carbon black was treated with strong acids following a wet oxidation procedure. An anal-ysis of the resulting particle surface chemistry and electrophoretic mobility was performed in evaluating colloidal stability. Changes in suspension microstructure due to oxidation were observed using small -angle X-ray scattering. Utilizing rheo-electric measurements, the evolution of the viscosity and conduc-tivity of the carbon black suspensions as a function of shear rate and carbon content was thoroughly stud-ied. Findings: The carboxyl groups installed on the carbon black surface through oxidation increased the sur-face charge density and enhanced repulsive interactions. Electrostatic stability inhibited the formation of the large-scale agglomerates in favor of the stable primary aggregates in suspension. While shear thin-ning, suspension conductivities were found to be weakly dependent on the shear intensity regardless of the carbon content. Most importantly, aqueous carbon black suspensions formulated from electrostat-ically repulsive primary aggregates displayed a smaller rise in conductivity with carbon content com-pared to those formulated from attractive agglomerates. (c) 2022 Elsevier Inc. All rights reserved.

Automated summary

The macroscopic properties of carbon black suspensions are mainly determined by the microstructure of agglomerates built of primary aggregates. Colloidal stability plays a crucial role in influencing their viscosity and conductivity. Experimental analysis revealed that treating carbon black with strong acids and wet oxidation resulted in changes in particle surface chemistry and electrophoretic mobility, indicating colloidal stability. Small-angle X-ray scattering was used to observe changes in suspension microstructure due to oxidation. Rheo-electric measurements showed that the viscosity and conductivity of carbon black suspensions were affected by shear rate and carbon content. Aqueous carbon black suspensions formulated with electrostatically repulsive primary aggregates exhibited a smaller increase in conductivity with carbon content compared to those formulated with attractive agglomerates.