Dependence of fragmentation behavior of colloidal aggregates on their fractal structure

Abstract

The fragmentation dynamics of aggregate of non-Brownian particles in shear flow is investigated numerically. The breakup behaviors of aggregates having the same connectivity but the different space-filling properties are examined. The Lagrangian particle simulation in a linear flow field is performed. The effect of surrounding fluid on the motion of multiple particles is estimated by Stokesian dynamics approach. The inter-particle force is calculated from the retarded van der Waals potential based on the Lifshitz theory. The results obtained in this work indicate that the fragmentation behavior of colloidal aggregates depends on their fractal structure. However, if the resultant aggregate size is smaller than the critical one, the fragmentation behavior shows the universality regardless of their original structure. Furthermore, the restructuring of aggregate in shear flow and its effect on the fragmentation process are also discussed

Strength Deterioration of Nonfractal Particle Aggregates in Simple Shear Flow

“…For the establishment of 6 these models, basic and quantitative understanding of aggregate dynamics in fluid flow has been required. 7 One of the most important issues is the interaction between fluid and aggregate, particularly the 8 fragmentation process of aggregate under fluid stress. Many fragmentation models have been proposed from 9 various point of view, in chronological order, the spherical model based on the balance between the internal 10 strength and fluid stress 2 , the model assuming two equal-sized spheres 3 , the model considering the permeable 11 fluid stress 4,5 , the model considering the spatial variance of internal strength 6 , and so on.…”

“…The first topic concerns the dispersion behavior of an isolated aggregate in 17 flow field. The relation between mass distribution of fragments and fluid stress has been discussed [7][8][9][10] . The 18 second topic is regarding the fluid force and the resultant internal stress on a rigid (non-deformable) 19 aggregate in fluid flow [11][12][13][14][15] .…”

“…Consequently, the fragmentation behavior of aggregates varies widely even though 7 they have similar space-filling properties 25,26 . The knowledge of such restructuring processes of aggregate 8 could be fed back to the kinetic models as a constitutive relation for the breakup process 27,28 . 9 The restructuring of non-fractal aggregate frequently occurs under the condition that the aggregate 10 strength is comparable with the fluid stress.…”

“…(2), the instantaneous position of 2 each particle is calculated. 3 The properties of primary particles and surrounding fluid are considered to be the same as those in our 4 previous work 8 . We assumed that primary particles are perfectly smooth spheres with the diameter d (=2a) 5 =650nm.…”

“…Pa·s. The inter-particle force is an attractive van der Waals force calculated from the retarded van 8 der Waals potential based on the Lifshitz theory 32 . The corresponding non-retarded Hamaker constant is 9 21 10 68 .…”