Modeling the Mechanism of Coagulum Formation in Dispersions

Abstract

The stability of colloidal dispersions is of crucial importance because the properties of dispersions are strongly affected by the degree of coagulation. Whereas the coagulation kinetics for quiescent (i.e., nonstirred) and diluted systems is well-established, the behavior of concentrated dispersions subjected to shear is still not fully understood. We employ the discrete element method (DEM) for the simulation of coagulation of concentrated colloidal dispersions. Normal forces between interacting particles are described by a combination of the Derjaguin, Landau, Verwey, and Overbeek (DLVO) and Johnson, Kendall, and Roberts (JKR) theories. We show that, in accordance with the expectations, the coagulation behavior depends strongly on the particle volume fraction, the surface potential, and the shear rate. Moreover, we demonstrate that the doublet formation rate is insufficient for the description of the coagulation kinetics and that the detailed DEM model is able to explain the autocatalytic nature of the coagulation of stabilized dispersions subjected to shear. With no adjustable parameters we are able to provide semiquantitative predictions of the coagulation behavior in the high-shear regions for a broad range of particle volume fractions. The results obtained using the DEM model can provide valuable guidelines for the operation of industrial dispersion processes.

Size and Structure of Clusters Formed by Shear Induced Coagulation: Modeling by Discrete Element Method

“…16 We have already shown that in our simulations the exponent was equal to −0.65 ± 0.075, which is close to the scaling predicted by Equation 19.…”

“…19 This enables us to study the effect of the elasticity and adhesion of the primary particles on the properties of the clusters. The model is spatially three-dimensional and we implemented the two-way coupling between particles and flow to capture the hydrodynamic interactions.…”

Numerical investigation of hard-gel microparticle suspension dynamics in microfluidic channels: Aggregation/fragmentation phenomena, and incipient clogging

“…The Johnson-Kendall-Roberts (JKR) [24] model for particle-particle adhesion/collision is employed. A number of works available in the literature have used this contact model for simulating aggregation/fragmentation process of particulate aerosol systems [16,17] and, more recently, cluster formation in shear-induced coagulation in a system made by hard spherical particles in water [25,26]. To the best of our knowledge, however, this is the first time that aggregation/breakage phenomena are studied for a system made by a water suspension of hard-gel particles flowing in a microfluidic device.…”

Coupling of CFD Simulations and Population Balance Modeling to Predict Brownian Coagulation in an Emulsion Polymerization Reactor

“…The production of many polymers often involves stages in which the monomer, polymer, or the intermediate products are dispersed into small particles. This adds a certain number of challenges that are mainly related to the colloidal stability of the latex . Unwanted particle coagulation is a major cost to the latex manufacturing industry mainly because of its negative effect on the product quality, product loss, and reactor down time.…”

“…This adds a certain number of challenges that are mainly related to the colloidal stability of the latex. [29] Unwanted particle coagulation is a major cost to the latex manufacturing industry mainly because of its negative effect on the product quality, product loss, and reactor down time. On the other hand, the ability to perform controlled coagulation in other circumstances is desirable, and it is important to be able to predict the impact of mixing and species concentrations in this particular case.…”