Evolution of Aggregate Shape in Simulation of Dense Aggregating Systems
Abstract
Aggregate shape is studied by off-lattice Monte-Carlo simulations of cluster-cluster aggregation, for systems that start out dilute and become dense. Shape is quantified by looking at the degree of shape anisotropy, A_ij, defined as successive ratios of squares of the principle radii of gyration from diagonalization of the moment of inertia tensor. When dilute, aggregate shape for 3d diffusion-limited, ballistic-limited and reaction-limited aggregation classes is self-preserving and in rough agreement with the Hierarchial model. We find quite good agreement between 2d simulation results and past experiments on aggregating polystyrene spheres. The effective density of aggregates is quantified by calculation of the aggregate volume fraction f_v^c. When f_v^c ∼= p_c, where pc is the 3d site percolation threshold, A_ij begins to decrease. This decrease continues up to the gel point where aggregate shape becomes equivalent to that of 3d site percolation clusters, in the vicinity of the percolation threshold. For all aggregation classes and all times, we find that A_ij is independent of monomer volume fraction f_v. Furthermore, results imply that in particulate systems, aggregate shape anisotropy is bound above by the Hierarchial model and below by site percolation.
- Publication:
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APS March Meeting Abstracts
- Pub Date:
- March 2003
- Bibcode:
- 2003APS..MARN13001F