Does Shape Anisotropy Control the Fractal Dimension in Diffusion-Limited Cluster-Cluster Aggregation?

摘要

Motivated by recent experiments of soot formation in premixed flames where a minority population of the “stringy” aggregates is found to have a fractal dimension as low as 1.2 instead of the classic diffusion-limited cluster-cluster aggregation (DLCA) value of 1.8, we address this same question in our simulation study: is there a distribution of fractal dimensions in a given ensemble of aggregates and does shape anisotropy of clusters control the fractal dimension? Our results, however, clearly show classic DLCA yields aggregates of a broad range of shapes all with D_f≈1.8 independent of their shape, but with a shape dependent pre-factor k₀ , in the relation between radius of gyration R_g , mass N, monomer radius a, and fractal dimension . Thus the pre-factor k₀ gains in status as a descriptor of aggregate morphology so that aggregates should be described by the pair of parameters D_f and k ₀ , i.e., (D_f, k₀).