In situ study of the dynamics of erosion of carbon black agglomerates

With the help of a counter-rotating transparent rheometer equipped with an optical microscope, the erosion of single, commercial carbon black agglomer ates suspended in a polyisobutylene fluid was accurately recorded in situ. We observed that clouds of very small aggregates were leaving the agglomera te at 45 and 225 degrees in the shear gradient-flow direction plane, where the stress is maximum. The distribution of the arrached aggregates is more efficient when the carbon black agglomerate is more asymmetric. A spherical agglomerate of critical radius R-o will reach a radius R-t at time t follo wing R-o(3) - R-t(3) = at, a being a constant. This implies that the rate a t which the number of aggregates is leaving the agglomerate is a constant, independent of the size of the agglomerate. (C) 2001 John Wiley & Sons, Inc . J Appl Polym Sci 80: 1627-1629, 2001.