The particle characteristics in a suspension affect the performance and quality of the end product of many chemical industries. The shape of the suspended particles can be influenced by changes in the manufacturing process conditions. Thus, there is a need for a robust method for continuous monitoring of particle characteristics through the process. This study investigates the feasibility of using spatially and angularly resolved diffuse reflectance measurements as a method of determining particle shape. A forward calculation was developed using the discrete dipole approximation to estimate optical properties of the single particle and the diffuse approximation for the reflectance of the particle suspension. The method was used to study aqueous suspensions of randomly-oriented polystyrene ellipsoids. Our objectives were to determine and elucidate the contribution of aspect ratio on optical measurement in vis-NIR spectra. The results suggest that the method is suitable for determining particle shape for suspensions where the particle and the solvent have significantly different optical properties. For these systems, the study suggests that diffusion reflectance measurements can be developed into an in-line method for particle shape determination.
We employ a physical theory to construct a computational model that accounts for both multiple scattering and absorption of light. The approach does not require a calibration model. Mie theory to describe single particle scattering, which is combined with the diffuse approximation to the radiative transfer equation to provides an analytical prediction of the reflectance. This approach is applied to experimental reflectance measurements on polystyrene particle suspensions with a wide range of particle radii and volume fractions. The method provides good estimates of the suspension properties from a full NIR-vis-UV spectrum.