Small-angle scattering by fractal aggregates: A numerical investigation of the crossover between the fractal regime and the Porod regime

Fractal aggregates are considered computationally using off-lattice cluster-cluster aggregation models. The aggregates are made of spherical particles of different sizes distributed according to a Gaussian-like distribution characterized by a mean a₀ and a standard deviation {σ}. The wave-vector-dependent scattered intensity I(q) is computed in order to study the influence of the particle polydispersity on the crossover between the fractal regime and the Porod regime. It is shown that, given a₀, the location qc of the crossover decreases as {σ} increases. The dependence of qc on {σ} can be understood from the evolution of the shape of the center-to-center interparticle-distance distribution function.