Relevance of light scattering theory in photon correlation spectroscopic experiments

Since photon correlation spectroscopy (PCS) is essentially a light scattering technique, it estimates the intensity-weighted particle size distribution. Using the Mie theory, some consequences were demonstrated. First, argon ion lasers were shown to be superior for particle sizing of very small particles. In addition, multiple scattering was shown to be largely dependent on the scattering angle and the state of polarization of the light source. Owing to this disturbing phenomenon, sizing of super-micron particles becomes troublesome. The estimated intensity distribution of polydisperse samples could be greatly influenced by the observation angle. The use of simplified light scattering theories such as the Rayleigh and the Debye-Gans theory was shown to be limited to small particles, especially in the case of high refractive indices. Finally, it was shown that the smoothing effect of PCS data analysis software may give rise to artificial bimodal number- or weight distributions, even when the Mie theory is considered