Time-scale separation in thixotropic structural rebuilding of carbon black suspensions revealed by rheo-impedance measurements

In this study, carbon black (Ketjen Black) suspensions were employed as model non-Newtonian particulate systems to investigate shear-history-dependent structural reconstruction dynamics using a rheo-impedance approach. Slurries dispersed with poly(vinylpyrrolidone) (PVP) of different molecular weights and concentrations exhibited pronounced shear-thinning behavior, and both the magnitude of shear thinning and the power-law index strongly depended on dispersant concentration and molecular weight. Step shearing tests revealed that particle networks disrupted under high shear were rebuilt after shear cessation. Under steady shear conditions, a clear inverse correlation was observed between the relative viscosity ηr and the total electrical resistance RT, indicating that both responses reflect the same underlying particle-network structure through mechanical connectivity and electrically effective particle contacts. However, during the recovery process after shear cessation, the temporal evolutions of mechanical and electrical responses did not coincide. The recovery of the electrical network was delayed relative to that of the mechanical network, demonstrating decoupled recovery dynamics governed by distinct characteristic time scales. These findings highlight that structural rebuilding in non-Newtonian particulate suspensions cannot be described by a single kinetic process, but instead involves time-scale separation between mechanical network formation and electrically effective contact reformation. The rheo-impedance method provides a complementary tool for probing thixotropic structural reconstruction and offers new insight into the dynamics of particle-network rebuilding under shear.