(679g) Influence of the Potential Barrier on the Breakage of Colloidal Aggregates in Simple Shear and Elongational Flows

Influence of the Potential Barrier on the Breakage of Colloidal

Aggregates in Simple Shear and Elongational Flows

Zhiqiang Ren, Marco Lattuada

Adolphe Merkle Institute, University of Fribourg, Rte de lâ??Ancienne Papeterie, P.O. Box 209, 1723 Marly, Switzerland

Understanding the effect of interactions on the breakage of colloidal clusters is of crucial importance to better design nanoparticles redispersion and coagulation processes. In this work the colloidal aggregates under simple shear and elongational flows were analyzed by means of Stokesian Dynamics simulation. A library of clusters made of identical spherical particles covering a broad range of masses and fractal dimension values (from 1.8 to 3) have been generated by means of a combination of several Monte-Carlo methods. The hydrodynamic interactions among the particles have been accounted for by Stokesian Dynamics. DLVO theory has been used to describe the interparticle interactions, while contact forces, described by means of discrete element method, have been included to provide the clusters with realistic structural rigidity. The aggregates breakage process was investigated by exposing them into a well-defined shear forces, generated under both simple shear conditions and elongational flow. To investigate the evolution of aggregate size and morphology, respectively, the mean radius of gyration and the cluster fractal dimension were monitored during the breakup process. Considerable attention has been given to understand the effect of electrostatic repulsive interactions and on primary particle size on both the breakage rate and cluster fragment mass distribution. It has been found that the breakage rate of clusters was controlled by the potential barrier between particles that was dominated by DLVO theory. A semiempirical equation that related to potential barrier and the breakage rate has been proposed.