Relevance of aggregate anisotropy in sheared suspensions of carbon black

Abstract

Carbon black is a filler frequently used in conductive suspensions or nanocomposites, in which it forms networks supporting electric conductivity. Although carbon black aggregates originate from a presumably isotropic aggregation process, the resulting particles are inherently anisotropic. Therefore, they can be expected to interact with shear flow, which significantly influences material properties. In this study, we investigate sheared suspensions of carbon black aggregates to elucidate the impact of aggregate anisotropy on the rheological properties. We aim at concentrations below and above the conductivity percolation threshold and comprehensively characterize particle behavior under flow conditions. Aggregates assembled by a diffusion-limited aggregation process are simulated with Langevin dynamics in simple shear flow. The simulations reveal a clear alignment of the aggregates’ long axis with the flow direction, an increase in tumbling frequency with higher shear rates, and a shear-thinning response. This behavior closely parallels that of rod-like particles and underlines the significance of the anisotropic nature of carbon black aggregates. These findings will facilitate the optimization of nanocomposite precursor processing and the tailoring of carbon black–based conductive suspensions.