(78a) Aggregation and Breakage of Polystyrene Particles under Turbulent Conditions: Dynamic Experiments

Aggregation of fully destabilized polystyrene particles under turbulent conditions in a stirred tank was studied experimentally. Two independent moments of the cluster mass distribution (CMD), namely mean radius of gyration and zero angle intensity, were obtained from online static light scattering measurements. In our experiments we covered the range of solid volume fractions from 1 to 40 ppm and the range of volume average shear rates from 100 to 1400 s-1, while two different sizes of primary particle (290nm and 810nm) were used. The hypothesis that steady state CMD is controlled by the dynamic equilibrium between aggregation and breakage, and therefore is not dependent on the aggregation path, was tested experimentally. First, the batch experiment was performed till the steady state was reached in order to eliminate restructuring effects. Afterwards, starting from the particular initial conditions corresponding to this steady state, we monitored the dynamic response of the system on the perturbations of one or more system parameters (solid volume fraction, G) till the system relaxed to a new steady state. In addition, when the timescale of the perturbations is larger then the timescale of the aggregation and breakage one can obtain information about steady state CMD as a function of the system parameters along the perturbation path. Based on these assumptions, dynamic experiments were designed and carried out to test their soundness by comparing moments of the steady state CMDs at the same solid volume fraction and G obtained for different initial conditions as well as via different paths. The results show experimental evidence that steady state CMD (at least for the system considered in this work) is controlled by dynamic equilibrium between aggregation and breakage.