(304a) Breakage of Colloidal Aggregates in Shear Flow

Authors: 
Harshe, Y. M., ETH Zurich
Morbidelli, M., Institute of Chemical and Bioengineering, ETH Zurich


Abstract:

The aggregation, breakage, and restructuring of colloidal clusters have been studied thoroughly in literature through both modeling and experiments. The cluster behaviour in different flows and scaling laws for cluster size on flow parameters for clusters with great variety of cluster geometries has been reported by many researchers. In due of these extensive efforts in modeling, the fundamental understanding of cluster breakage is still incomplete due to the fact that none of the efforts accounted both hydrodynamic particle-particle interactions in detail. Surprisingly, even after the experimental evidence of bending moment presented by Pantina and Furst[1], there are only a few simulation studies where the tangential contact forces are correctly included. In addition, almost no contribution has been published where rigorous simulations have been performed to investigate the dependence of the time required for the on-set of cluster breakage and fragment size distribution on cluster size, structure, shear rate, and inter-particle interactions. In order to correctly predict the fate of a colloidal cluster in a fluid flow both hydrodynamic and inter-particle interactions should be accounted correctly.

In the present work, we have used the Stokesian dynamics method developed by Brady and Bossis[2], which allows computation of the full hydrodynamic interactions between particles. The inter-particle interactions were introduced through the DLVO theory. To account for the contact forces the tangential force model suggested by Becker and Briesen[3] was implemented. Simulations were performed for various cluster sizes with different fractal dimensions, generated using a combination of different Monte-Carlo methods, under different flow conditions such as gravity, simple shear, and elongational flow. The developed model was first used to investigate the dependence of time required for the on-set of cluster breakage on the cluster geometry (structure and size) and primary particle size for various Peclet number values. Precious information on the fragment size distribution has been also obtained.

Keywords:

Aggregation, breakage, Stokesian dynamics, tangential forces

References:

[1] Pantina, J.P., and Furst, E.M., Langmuir, 22, 5282, 2006

[2] Brady, J.F., and Bossis, G., J, Ann. Rev. Fluid Mechanics, 20, 111, 1988

[3] Becker, V., and Brisen, H., Phy. Rev. E, 78(6), 061404, 2008