(198g) Experimental Investigation of Breakage of DLCA Colloidal Aggregates in Shear and Elongational Flows

Breakage and/or reconstructing of colloidal aggregates are encountered in the processing of colloidal suspensions. The final average aggregate size and aggregate size distribution is decided by the initial aggregates' size, imposed flow field, and very importantly the initial structure of the aggregates. Except few systematic experimental studies scarcely some literature has been devoted in this study. The dynamic evolution of such aggregate properties could be used to have an insight into the kinetics of the breakage mechanism. The understanding of this process enables to estimate some lumped parameters which can then be used in Population Balance Equations as breakage kernels.

In the present attempt we have focused our attention to pure breakage process of Diffusion Limited Cluster Aggregates (DLCA) in shear and elongational flows. Initially, DLCA aggregates are produced by carrying diffusion limited cluster aggregation starting with different primary particle sizes to produce aggregates of a specific size. The aggregates were then exposed to various shear rates for both shear and elongational flows. The time evolution of fractal dimension (D¬f) and radius of gyration (Rg) was tracked by light scattering measurements and image analysis technique, wherever possible. The obtained data was compared with the previous literature and new scaling laws were defined. The results were qualitatively compared with the Stokesian dynamic modeling.

Keywords:

Breakage, DLCA, aggregates, Stokesian dynamics