Population balance modelling for high concentration nanoparticle sizing with ultrasound spectroscopy

Ultrasound particle sizing is attracting an increasing attention from academic research and industrial applications as it offers non-invasive, suitable for highly turbid and concentrated nanoparticle suspensions and potentially no sample dilution needed features. The main challenge to this technique is thought to be its capability of dealing with high concentration. Most ultrasound particle sizing techniques employ ECAH (Epstein, Carhart, Allegra and Hawley) theory based models for the inversion of ultrasound spectra to particle size distribution (PSD). However, this theory is based on "single particle scattering", namely a single particle immersed in an infinite medium, it is therefore only valid when ultrasound attenuation and particle concentration are linearly related. With the increase of particle concentration, due to the interactions between particles, the relation between attenuation and concentration may become nonlinear for solid-liquid suspensions. This paper demonstrates a method using population balance (PB) modelling to deal with the high concentration PSD problem for silica suspensions. It concludes that with a de-aggregation model, it is possible to convert attenuation inverted PSDs (ECAH model based inversion) at high concentrations into the PSD that is thought to be the correct PSD at a critical low concentration by a PB simulation.