Particle size distribution effects on the light scattering properties in non-diluted colloidal suspensions: A numerical study

The static light scattering technique potentially offers a nondestructive evaluation of a particle size distribution in dense colloidal suspensions. Understanding the size distribution's correlation with the light scattering properties and modeling electromagnetic scattering with high accuracy and efficiency are crucial for technique development. The polydisperse dependent scattering theory (DST) is an accurate model, but its calculation is costly. We aim to numerically examine the size distribution effects on the scattering properties of dense suspensions up to the volume fraction of 20% in the near-infrared wavelength of 600-1000 nm using three electromagnetic models: the polydisperse and monodisperse DST, and the local monodisperse approximation (LMA). We considered various size distributions in Gaussian and logarithmic forms with constant standard deviations of 21 nm and 101 nm in the mean diameter range of 75-700 nm by shifting the distribution while keeping its shape. We showed that the monodisperse approximation is invalid at a small mean diameter of less than 200 nm, even at the sharp Gaussian distribution. It suggests the strong size distribution effects. Meanwhile, the approximation holds at a large diameter of more than 650 nm, even at the broad logarithmic distribution. We showed that the LMA results nicely agree with the polydisperse DST results for all the current conditions. At the same time, the LMA calculations are over a thousand times faster than the polydisperse DST because the LMA reduces the sum calculation over particle diameter pairs. Thus, the LMA is a great candidate for the electromagnetic model.