Measurement of Static and Dynamic Light Scattering

Using the SLS technique, the size distribution can be measured accurately when the Rayleigh-Gans-Debye approximation is valid for dilute homogenous spherical particles in dispersion. For the commercial samples, the static sizes are consistent with the sizes provided by supplier respectively. The values of root mean square radius of gyration measured using the Zimm plot and calculated using the commercial size distributions or size distributions measured using the SLS technique are consistent respectively. Based on the static size distribution, with one assumption between the static and hydrodynamic radii, the calculated and measured data of DLS are consistent very well at all the scattering angles investigated respectively. Using the static size information the dimensionless shape parameter is discussed, our results show that the shapes can not be determined based on the dimensionless shape parameter. Traditionally, the particle information: apparent hydrodynamic radius and polydispersity index are obtained from DLS by analyzing the deviations of the intensity-intensity autocorrelation function from an exponent function. Since the apparent hydrodynamic radius obtained using the Stokes-Einstein relation is an optical weighted average radius, it is an approximate value of mean hydrodynamic radius. And the polydispersity index is not relate to the width of hydrodynamic radius. Therefore the apparent hydrodynamic radius and polydispersity index cannot give an accurate description for size distribution.