Dispersion of carbon black in a continuous phase: Electrical, rheological, and morphological studies

Abstract

This work investigates the dispersion of carbon black (CB) aggregates into various polymeric matrices to increase electric conductivity. The effect of matrix viscosity on CB morphology and, consequently, on the blend conductivity was thoroughly addressed. The electric conductivity increases from 10–9 to 10–4 when less than 3% CB aggregates were dispersed into the PDMS liquid of various viscosities. The CB threshold loading was found to increase from 1% to 3% as the viscosity rose from 10 cp to 60 000 cp. This finding shows that an ideal loading with CB aggregates is far below that (generally 15%) of a typical pelletized CB loading. Moreover, the microscope and RV tests reveal that CB aggregates diffuse and form an agglomerate-network when the conductivity threshold is reached in a low-viscosity matrix. However, a CB aggregate-network was observed when the threshold value was attained in a high-viscosity matrix. These two mechanisms can be distinguished at approximately 1000 cp. Finally, experimental observation shows that the increase of viscosity during curing does not influence the conductivity of the composite while the CB aggregates dispersed in a thermoset matrix. The minimum viscosity during curing, however, was found to be critical to CB dispersion morphology and, consequently, to ultimate electric conductivity.