New Interpretation for Laser Light Scattering Technique

Abstract

The new method proposed in this work not only measures the particle size distribution and the average molar mass accurately using the static light scattering (SLS) technique when the Rayleigh-Gans-Debye approximation is valid for dilute poly-disperse homogenous spherical particles in dispersion, but also enables us to have insight into the theoretical analysis of the dimensionless shape parameter $ρ$. With the method, a new size, static radii $R_{s}$, can be measured. Based on the new static particle size information, detailed investigation of the normalized time auto-correlation function of the scattered light intensity $g^{(2)}(τ)$ reveals that there exist three different particle sizes: the static radius, hydrodynamic radius and apparent hydrodynamic radius that is the hydrodynamic radius obtained using the cumulants method. With a simple assumption that the hydrodynamic radius $R_{h}$ is in proportion to the static radius $R_{s}$, the expected values of $g^{(2)}(τ) $ calculated based on the static and commercial particle size information are consistent with the experimental data. With the assistance of simulated data, the apparent hydrodynamic radius is discussed. The results show that the apparent hydrodynamic radius is different from the mean hydrodynamic radius and is determined by the optical, hydrodynamic characteristics and size distribution of particles and scattering vector. The analysis also reveals that $ρ$ is determined by not only the structure of particles but also the relationship between the optical and hydrodynamic characteristics of particles even for mono-disperse model.