Turbidimetric determination of particle size distributions of colloidal systems

Abstract

Application of the Mie theory of light scattering to measurements of the turbidity ratio and the wavelength exponent provides an easy method for estimating particle size distributions of nonabsorbing isotropic spheres in the micrometer to submicrometer range. Combining both these light-scattering techniques not only allows one to analyze particle sizes which are too large for quasi-elastic light scattering and too small for optical microscopy, but can be accomplished with only two turbidity measurements and no prior knowledge of the particle volume fraction. An algorithm is presented for constructing turbidity spectra, for any system of known optical constants and known distributional form, which can be used to easily determine the mean diameter and standard deviation of an unknown distribution. Using this algorithm, size-distribution curves were obtained from turbidity measurements at two widely separated wavelengths. These distributions are in agreement with distributions determined from scanning electron microscopic analysis.