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Abstract: Nanoparticle agglomeration in a quiescent fluid is simulated by solving theLangevin equations of motion of a set of interacting monomers in the continuumregime. Monomers interact via a radial, rapidly decaying intermonomerpotential. The morphology of generated clusters is analyzed through theirfractal dimension $d f$ and the cluster coordination number. The time evolutionof the cluster fractal dimension is linked to the dynamics of two populations,small $k \le 15$ and large $k>15$ clusters. At early times monomer-clusteragglomeration is the dominant agglomeration mechanism $d f = 2.25$, whereasat late times cluster-cluster agglomeration dominates $d f = 1.56$. Clustersare found to be compact mean coordination number $\sim 5$, tubular, andelongated. The local, compact structure of the aggregates is attributed to theisotropy of the interaction potential, which allows rearrangement of bondedmonomers, whereas the large-scale tubular structure is attributed to itsrelatively short attractive range. The cluster translational diffusioncoefficient is determined to be inversely proportional to the cluster mass andthe per-unit-mass friction coefficient of an isolated monomer, a consequenceof the neglect of monomer shielding in a cluster. Clusters generated byunshielded Langevin equations are referred to as \textit{ideal clusters}because the surface area accessible to the underlying fluid is found to be thesum of the accessible surface areas of the isolated monomers. Similarly, idealclusters do not have, on average, a preferential orientation. The decrease ofthe numbers of clusters with time and a few collision kernel elements areevaluated and compared to analytical expressions.



Author: Lorenzo Isella, Yannis Drossinos

Source: https://arxiv.org/



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