Kinetics of turbulent coagulation studied by means of end-over-end rotation.

We have investigated the kinetics of coagulation of monodisperse polymer latices in turbulent flow, with the purpose of characterizing the flow in terms of the frequency of flow-induced (orthokinetic) collisions. We chose a very simple and practically convenient way to generate turbulent flow, namely by pouring dispersions from one small bottle into another, which is equivalent to rotating such bottles end over end. This method allows us to do experiments for times as short as 1 s, thus giving access to the initial stages where binary collisions of primary particles ("monomers") are dominant. The total number concentration of aggregates, as well as the size distribution of clusters, was measured as a function of the number of mixing steps by means of a single particle optical sizer (SPOS). The data were analyzed assuming additivity of the perikinetic and orthokinetic coagulation rates, taking into account the effect of hydrodynamic interaction. The dependence of the rate of coagulation on the size of primary particles was found to agree fully with theoretical predictions, thus providing clear evidence that the proposed method works, i.e., the adopted simple procedure yields quantitatively reproducible and detailed kinetic data on collision frequencies. This is of importance for subsequent studies of other rapid aggregation processes such as, e.g., bridging flocculation by polymeric flocculants.