Frequency domain photon migration for the characterization of concentrated particulate suspensions

The goal of this research was to develop photon migration as a potential tool for the on-line characterization of particulate suspensions. In this study, the process of determining the particle size distribution and volume fraction a colloidal suspension by the inversion of frequency domain photon migration measurements of the isotropic scattering coefficient is demonstrated on dilute and concentrated polystyrene latices and titanium dioxide suspensions. Measurements were performed at wavelengths between 450 nm and 835 nm on unimodal polystyrene latices with mean diameters between 100 nm and 600 nm. The volume fractions of the latices ranged from 1% to 35%. Upon the utilization of the Percus-Yevick hard sphere model for the static structure factor, significant improvement was shown in the recovery of the mean diameter and volume fraction in high volume fraction latices. No other current sizing technique can make these measurements in concentrated suspension without system dependent calibration. Frequency domain photon migration (FDPM) has the advantage of self-calibration which makes it suitable for on-line measurement. To demonstrate this on-line capability, a batch emulsion polymerization reactor was constructed and FDPM measurements made during the formation of polystyrene latices in unseeded and seeded reactions