Accounting for constituent particle polydispersion in the determination of the volume specific surface area equivalent diameter

Abstract

First introduced by Kreyling et al. (2010), the Volume Specific Surface-Area (VSSA) has been identified as a relevant and alternative method to electron microscopy to determine whether a material is a nanomaterial or not, in addition to being mentioned in the definition from the European Commission. This parameter was recently integrated as a tier 1 screen in the JRC decision trees. VSSA is an integral measurement method that provides particle size indirectly. When the conversion from specific surface area to particle diameter is performed, the primary particles are assumed to be spherical and monodisperse. This strong assumption is far from reality. The study consisted in evaluating the influence of the polydispersion of the constituent particles of a material on its specific surface, and in proposing a methodology allowing it to be considered in the conversion of the VSSA into equivalent diameter of constituent particles. This correction was applied to eight powders, with a median diameter in number between 9 and 130 nm, and under the assumption of a distribution according to a normal law. The results indicate that considering the polydispersion improves the determination of the equivalent diameter, the relative deviations compared to the reference measurements in electron microscopy being between -9% and 18%.