Determination of Particle Size and Number Density of Opaque Colloidal Mixtures Using Diffuse Photon Density Waves and Two-Wavelength Light Sources

Abstract

A diffuse photon density wave (DPDW) propagates as a spherical energy wave in highly scattering media, such as opaque colloidal mixtures. The advantage of using DPDW is that the absorption and reduced scattering coefficients of the opaque colloidal mixtures can be measured without dilution and calibration. We propose a method for the estimation of the mean particle size and number density of the opaque colloidal mixtures using the relationship between estimated values and optical properties. In this study, we first determined the mean particle size and number density of colloidal silica, a single-particle dispersive medium, to confirm the validity of the method and evaluated the accuracy of the measurement. Then, we determined the mean particle size and number density of casein micelles and fat globules in milk, which is regarded as a typical opaque colloidal mixture, using two light sources with different wavelengths.