Role of Particle-Particle Interaction Towards Effective Interpretation of Z-Average and Particle Size Distributions from Dynamic Light Scattering (DLS) Analysis

Despite the widespread utilization of Dynamic Light Scattering (DLS) as an analytical tool for particle sizing, one of the critical questions raised among the users is on how to do proper analysis and interpretation of the data obtained. In view of this, the present work was done to reveal the role of particle-particle interaction towards the interpretation of Z-average and the three types of particle size distributions (intensity-weighted, volume-weighted, and number-weighted) obtained from DLS analysis. Experimental results showed that Z-average for the weakly-interacting (highly stable) SiO2 particles obtained from DLS was almost identical to that gained from TEM analysis. Meanwhile, for the strongly-interacting (non-stable, aggregating) bare Fe3O4 particles, the Z-average obtained from DLS was similar to 10 times larger than TEM result. In term of particle size distributions, it was found that all the three types of size distributions were closely collapsed into a single bell curve for the unimodal and monodisperse SiO2 particles; while for bare Fe3O4 particles which had been aggregated into polydisperse structures, the three size distributions exhibited large variation from each other. This observation implies that choosing the right size distribution become challenging in the latter case. Additionally, it was found that the Z-average of bare Fe3O4 particles varied significantly with the particle concentration used for DLS measurement. Concerning with particle aggregation kinetic, results from three independent case studies showed that the intensity-weighted distribution provides more logical and consistent right shifting as compared to both volume-weighted and number-weighted distributions.