EFFECT OF POLYMERS ON THE AGGREGATION KINETICS AND FRACTAL STRUCTURE OF CARBON-BLACK SUSPENSIONS IN AN ALIPHATIC SOLVENT - A STATIC AND DYNAMIC LIGHT-SCATTERING STUDY

The aggregation kinetics of suspensions of three kinds of carbon black 100N basestock is studied by static and dynamic light scattering techniques. It is found that two of the carbon blacks, Vulcan 9 and 3, aggregate according to a diffusion limited cluster aggregation process. Their fractal dimensions are found to be 1.75 and 1.85 respectively. The kinetics of the third one, Sterling V, is found to correspond to a reaction limited cluster aggregation, giving a cluster fractal dimension, df = 2.15. Vulcan 9 suspensions in 100N basestock are also studied in the presence of a polymer at two different concentrations corresponding to R = 0.3 and R = 3, where R is the mass ratio of polymer to carbon black. Two polymers, differing only by the presence or not of a dispersant function, are chosen. In the case of the polymer without dispersant, the aggregation rate is not greatly modified by the addition of a small amount of polymer (R = 0.3) compared to the suspension without polymer (R = 0). However, at the higher concentration (R = 3), the rate is reduced. The presence of the dispersant function significantly decreases the aggregation rate even at low polymer concentration (R = 0.3). Further, at the higher concentration (R = 3) the cluster size at the beginning of the kinetic process is smaller and remains constant throughout the whole experiment. These clusters can be considered as permanent structures which cannot be destroyed by stirring or ultrasonic action. The effect of polymers is interpreted in terms of steric and electrosteric repulsions.