Does shape anisotropy control the fractal dimension in diffusion-limited cluster-cluster aggregation?

Abstract

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 Df ≈ 1.8 independent of their shape, but with a shape dependent pre-factor k0, in the relation between radius of gyration Rg, mass N, monomer radius a, and fractal dimension Df, N = k0(Rg/a)Df. 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 Df and k0, i.e., (Df, k0). Copyright © American Association for Aerosol Research.