Precise measurement of particle size in colloid system based on the development of multiple-angle dynamic light scattering apparatus

Abstract

Dynamic light scattering (DLS) is a widely used, non-invasive and in-situ method for particle size measurement. However, the precision of the measurement results is still under discussion. Theoretically, the apparent hydrodynamic diameter measured by DLS varies with scattering angle due to Mie scattering as well as long-distance interaction between particles. In this paper, a multiple-angle dynamic light scattering (MDLS) apparatus is established. After determining the critical concentration at which multiple scattering occurs at different scattering angle, polystyrene latex (PSL) particles sized from 23 to 500 nm diluted with different concentrations are precisely measured at different scattering angles. By introducing special pin-holes, precise alignment design and beam-stops at all scattering angles, the precision of the MDLS apparatus is highly improved. DLS results are strongly angular and concentration dependent, and the trends vary with particle size. DLS results at infinite dilution and zero angle are obtained after extrapolation, which eliminates the effects of long-range interactions and intraparticle interference. The present optical design extends the application validity of this method from nano particle to submicron particle.