Numerical investigation of the possibility to determine the primary particle size of fractal aggregates by measuring light depolarization

In this paper, depolarization of light ρ=Ivh/Ivv by fractal aggregates of nanoparticles is considered as a possible way to infer the primary particles radius Rp. A numerical study makes it possible to evaluate the impact of optical and morphological parameters of fractal aggregates (number and size of primary spheres, fractal dimension, overlapping and necking effects) on depolarization ratio and a model is proposed. It appears that for large aggregates, an asymptotic behavior of the depolarization ratio as a function of qRp (q=4π/λ×sin(θ/2)) is established promoting the experimental measurement of Rp. Nevertheless, there is evidence that particle anisotropy, optical index, primary sphere overlapping and necking effects strongly impact the depolarization ratio. By taking into account all these parameters, a good correspondence is found between experimental and numerical results.

► We use the depolarization of light ρ=Ivh/Ivv for studying fractal aggregates. ► We examine a possible way for inferring the primary particles radius Rp. ► An experimental study with Ethylene soot and Palas soot have been achieved. ► A numerical study permits to evaluate the impact of fractal aggregates parameters. ► A model is proposed.