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Cluster Anisotropies in Colloidal Aggregation in the Presence of Gravity

By Gonzalez A.-E.


Monte Carlo simulations, Colloidal aggregation, SedimentationExtensive Monte Carlo simulations of colloidal aggregation, coupled with the sedimentation experienced preferentially by the large clusters, are performed. The stratification of the system, in the sense that the structural and dynamical quantities depend on the depth at which they are measured, and the acceleration of the aggregation rate followed by a slowing down, are confirmed [1]. In this work we describe a whole variety of cluster anisotropies that were not possible to describe in the previous paper [1], due to its letter-format size. We have found that in some cases of sedimentation strengths and layer depths (SSLD), (i) the large settling clusters are still self-similar making it possible to define a fractal dimension, substantially higher than the one of clusters produced by colloidal aggregation driven purely by diffusion (DLCA). In some other cases of SSLD we have found that (ii) the mean height and the mean width of the large settling clusters scale again as a power law with the cluster size, but with different scaling powers, leading to anisotropic self-affine clusters. Moreover, there are some other cases of SSLD for which (iii) only the mean width or the mean height of the large settling clusters scale as a power law with the cluster size, leading again to anisotropic clusters. Furthermore, there are also other cases for which (iv) neither the mean height nor the mean width scale as a power law with the cluster size, resulting once more in anisotropic clusters. Although in cases (ii), (iii) and (iv) we cannot define a fractal dimension, we feel that these large settling clusters should be more "compact", in a still undefined way, than the DLCA clusters. This is because they grow mainly by the sweeping of smaller clusters on their way downwards, which occlude the holes and cavities of these large clusters. [1] A. E. Gonzalez, Europhys. Lett. 73 (2006) 878

Topics: Monte Carlo simulations, Colloidal aggregation, Sedimentation
Publisher: TIMA Editions , Grenoble, France
Year: 2006
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Provided by: I-Revues

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