Influence of matrix infiltration on the dispersion kinetics of carbon black agglomerates

Abstract

The dispersion of carbon black agglomerates suspended in poly(dimethylsiloxane) liquids and subjected to simple shear flow has been studied. Two characteristic length scales that affect the dispersion process are identified and estimated from hydrodynamic drag coefficients measured in sedimentation experiments. One length scale, Lp, is a measure of the ease with which fluid can flow through the porous agglomerate structure and is directly related to its packing density and the morphology of the constituent particles. The second, δ, is a measure of the depth to which processing fluid has soaked into the agglomerate. Values of Lp were found to be relatively large for high structure carbon blacks and for low density agglomerates. The parameter δ varies with time of immersion in the processing fluid. Shearing experiments showed two kinetic regimes for the rate of dispersion. Analysis showed that fast dispersion occurred when Lp/δ exceeds a critical value and, conversely, relatively slow erosion occurred when Lp/δ is below a characteristic threshold value. For agglomerates having a density higher than a critical value, the kinetic regime shifts from fast to slow as the infiltration depth exceeds Lp after some shearing time. However, for agglomerates with a density lower than this value, erosion rates exceeded infiltration rates, Lp/δ remained greater than the critical ratio, and only fast erosion was observed.