Particle size analysis and beyond - laser diffraction and derived information regarding structures of mechano-fusion coated particles

Laser diffraction (LD) is widely used for the analysis of particle size distribution (PSD). Due to the structure of dry-coated mechano-fusion particle systems, the interpretation of the PSD remains challenging. This study investigates hetero-aggregate coating structures of alumina host particles (median diameter 43.3 μm) with polystyrene guest particles (average diameter 3.5 μm) in dry LD measurements and how dispersion conditions influence the PSD. Gentle freefall dispersion preserves coating structures and yields a monomodal PSD consistent with expected coated particle size. Differences in the PSD between samples of coated particles prepared under different process conditions are only observed using high-intensity dry dispersion. High-intensity dispersion alters the aggregation state by detaching guest particles, leading to bimodal PSD. The plateau values in the cumulative distribution furthermore exceed theoretical guest volume fractions. Experimental measurements are combined with simulations of diffraction patterns and inverse reconstruction. Simulations qualitatively support the experimental findings by linking particle arrangement and deformation to reconstructed PSD features. The apparent overrepresentation is attributed to guest particle deformation and comminution, biasing the volume-weighted PSD. Hence, LD provides more than particle size information: aggregation state, dispersion-induced changes, and guest particle deformation are revealed, enhancing the applicability of LD for quality control of dry-coated hetero-aggregates.