Characterization of Spherical Core-Shell Particles by Static Light Scattering. Estimation of the Core- and Particle- Size Distributions

Abstract

A numerical method is proposed for the characterization of core-shell spherical particles from static light scattering (SLS) measurements. The method is able to estimate the core size distribution (CSD) and the particle size distribution (PSD), through the following two-step procedure: i) the estimation of the bivariate core - particle size distribution (C-PSD), by solving a linear ill-conditioned inverse problem through a generalized Tikhonov regularization strategy, and ii) the calculation of the CSD and the PSD from the estimated C-PSD. First, the method was evaluated on the basis of several simulated examples, with polystyrene - poly(methyl methacrylate) core-shell particles of different CSDs and PSDs. Then, two samples of hematite - Yttrium basic carbonate core-shell particles were successfully characterized. In all analyzed examples, acceptable estimates of the PSD and the average diameter of the CSD were obtained. Based on the single-scattering Mie theory, the proposed method is an effective tool for characterizing core-shell colloidal particles larger than their Rayleigh limit without requiring any a-priori assumption on the shape of the size distributions. Under such conditions, the PSDs can always be adequately estimated; while acceptable CSD estimates are obtained when the core/shell particles exhibit either a high optical contrast, or a moderate optical contrast but with a high average core diameter / average particle diameter ratio.