(200f) Breakup Dynamics of Colloidal Clusters in Shear Flow

In this work, we present a broad spectrum computational study of the breakage dynamics of colloidal clusters in the presence of shear flow. We have formulated a model, which uses Stokesian dynamics to estimate the hydrodynamic interactions among the particles in a cluster, DLVO theory to describe the normal interparticle interactions, and tangential interactions through discrete element method to account for contact forces. Fractal clusters composed of monodisperse spherical particles were generated using different Monte Carlo methods, covering a wide range of cluster masses and fractal dimensions. The study is divided in to two parts, one related to first breakage events in colloidal clusters exposed to shear forces, while the second part focuses on their long term dynamics. The time required to reach the first breakage event of a cluster was used to compute a characteristic breakage rate constant for various flow magnitudes under simple shear conditions. The breakage rate constant showed a power law dependence on the product of the aggregate size and the applied stress, with values of the corresponding exponents depending only on the aggregate fractal dimension and the type of flow field, whereas the prefactor of the power law relation also depends on the size of the primary particles comprising a cluster. The long-term dynamics was quantified by monitoring the evolution of the average clusters size, fractal dimension, average particle coordination number and number of fragments. When the time was rescaled by the characteristic time for the first breakage event, the dynamics all clusters, independent of mass and fractal dimension, showed a universal behavior. The results of these simulations provide new insights on the complex interplay between cluster morphology and hydrodynamic and interparticles interactions in sheared dispersions of clusters.

References:

Harshe Y.M. and Lattuada M., Langmuir 2012, 28, 283–292

Harshe Y.M. and Lattuada M., Soft Matter, submitted