Comparison Between Theoretical and Experimental Turbidity Spectra of Medium and Large Size Monodisperse Polystyrene Latexes

Abstract

The particle size determination of dispersed materials by optical methods is largely used; the general trend consists in using angular light scattering and intensity fluctuation spectroscopy (1) methods, the analysis of turbidity spectra (2–7) receiving less attention. Nevertheless the latter method may also be worthwhile, but needs the knowledge of the refractive index of the dispersed material in the wavelength range 200–800 nm. If the refractive index values of bulk polystyrene are well known for λ > 400 nm, the literature data below 400 nm are not very reliable (8–11). In this paper, new measurements (20) of the refractive index of polystyrene are reported and tested by comparing calculated and experimental turbidity spectra of several PS hydrosols. It was then possible to describe the general behaviour from the U.V. to the near I. R. regions and to draw conclusions concerning the use of these results to determine the particle size of PS hydrosols.