New dynamic Zimm-type plot on light scattering measurement for evaluating interaction changes due to salt addition to particle dispersions

In dynamic light scattering (DLS) measurements of charged particle dispersions, the measured particle size may change depending on the scattering angles and particle concentrations. In this paper, we used polystyrene latex particles ranging from 100 nm to 30 nm to investigate the additional effect of adding NaCl aqueous solutions on particle size measurements by DLS. The smaller the particles, the higher the electrostatic shielding effect of charge in particle dispersion; however, it seems that the effect of salt addition, i.e., reducing the angular and concentration dependence, is apparently weaker for particles with larger size. By using the new dynamic Zimm-type plot proposed here, it is possible to evaluate the quantitative effect of salt addition and to derive accurate particle size for particle diameters 100 nm and smaller.