Rheo-dielectric behavior of carbon black suspensions

Rheo-dielectric behavior was examined for suspensions of two types of carbon black (CB) particles in varnish. For one type of CB particles having plain carbon surfaces, an agglomerated network was fully developed to exhibit low-frequency elasticity (under small strains) and high electrical conductance. This conductance decreased significantly under flow, reflecting flow-induced rupture of the network structure. This rheo-dielectric change well corresponded to the pseudo-plastic, non-Newtonian behavior of the viscosity eta, In contrast, for the other type of CB particles having oxidized carbon surface, only fragmented aggregates were formed. Correspondingly, this CB exhibited just moderate rheo-dielectric changes and weak nonlinearities in its eta. These results demonstrated the usefulness of the rheo-dielectric method for detecting the connectivity of the network composed of conductive CB particles.