Restructuring of colloidal aggregates in shear flow

Abstract

Abstract. A method to couple interparticle contact models with Stokesian dynamics (SD) is introduced to simulate colloidal aggregates under flow conditions. The contact model mimics both the elastic and plastic behavior of the cohesive connections between particles within clusters. Owing to this, clusters can maintain their structures under low stress while restructuring or even breakage may occur under sufficiently high stress conditions. SD is an efficient method to deal with the long-ranged and many-body nature of hydrodynamic interactions for low Reynolds number flows. By using such a coupled model, the restructuring of colloidal aggregates under shear flows with stepwise increasing shear rates was studied. Irreversible compaction occurs due to the increase of hydrodynamic stress on clusters. Results show that the greater part of the fractal clusters are compacted to rod-shaped packed structures, while the others show isotropic compaction.

Strength Deterioration of Nonfractal Particle Aggregates in Simple Shear Flow

“…20 Therefore we did not include the tangential force models in this simulation to avoid tuning parameters of the 21 simulation results. Although we can not mention for certain about the effect of tangential force on the 22 restructuring process of non-fractal aggregate at the present stage, the qualitative agreement between 23 numerical and observation results shown later ( Fig.3 and Fig.5) is a weak evidence of the less-significance of 24 tangential force to the discussion given here. 25 In our simulation, inertias of both particle and fluid are neglected on the assumption that the particle is 26 sufficiently small.…”

“…There have been a considerable number of researches on the dependence of the 20 fluid force on the aggregate structure and the distribution of the inter-particle force of the aggregate with an 21 open structure. 22 The last topic, the restructuring of an isolated aggregate by surrounding flow, usually represents the 23 change in space-filling property of aggregate by fluid stress and sometimes indicates the microscopic change 24 of bond distribution in the aggregate in the wider sense. Particularly the restructuring effect is enhanced in 25 shear flow.…”

“…In general, a soft matter in simple shear flow shows complicated structural change owing to both 26 rotation and elongation effects of the flow field, even though it has a simple chain-like or string-like structure 27 16,17 . There have been many numerical studies on the restructuring of aggregate in shear flow [18][19][20][21][22][23][24] . These 28 studies have reported that the magnitude relation between the bend stress by fluid force and the hold moment 1 by inter-particle force is important for the restructuring of fractal aggregate.…”

“…We 22 performed a Lagrangian-type simulation of the behavior of a non-fractal aggregate in shear flow by Stokesian 23 dynamics approach. The purpose of this study is to understand a detailed mechanism of the strength 24 deterioration of aggregate and to elucidate the role of rotation and elongation effects of shear flow on it. 25 Therefore we focus on the restructuring process for a specific condition that aggregate strength is comparable 26 to fluid stress and discuss it through the comparison with the existing experimental results and theoretical 27 models.…”

“…15 In this study, a tangential inter-particle force is not considered. It has been reported that the tangential 16 force occasionally plays a significant role on the deformation of fractal aggregate 20,21,24 . Therefore the 17 installation of tangential force model is possible to influence the simulation results on dynamic behaviors of a 18 non-fractal aggregate as shown here.…”