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 tech niques. It is found that two of the carbon blacks, Vulcan 9 and 3, agg regate according to a diffusion limited cluster aggregation process. T heir fractal dimensions are found to be 1.75 and 1.85 respectively. Th e kinetics of the third one, Sterling V, is found to correspond to a r eaction limited cluster aggregation, giving a cluster fractal dimensio n, df = 2.15. Vulcan 9 suspensions in 100N basestock are also studied in the presence of a polymer at two different concentrations correspon ding to R = 0.3 and R = 3, where R is the mass ratio of polymer to car bon black. Two polymers, differing only by the presence or not of a di spersant function, are chosen. In the case of the polymer without disp ersant, the aggregation rate is not greatly modified by the addition o f a small amount of polymer (R = 0.3) compared to the suspension witho ut 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 a t 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 ultrason ic action. The effect of polymers is interpreted in terms of steric an d electrosteric repulsions.