Particle sizing in strongly turbid suspensions with the one-beam cross-correlation dynamic light-scattering technique

The utility of the one-beam cross-correlation dynamic light-scattering system for sizing small particles in suspension was previously limited by its small-intensity signal-to-baseline ratio for strongly turbid suspensions. We describe three improvements in the optical system and sample cell that raise the ratio to a value comparable with that of other cross-correlation dynamic light-scattering systems. These improvements are (i) using a square cross-sectional sample cell to minimize the attenuation of the incident beam and singly scattered light, (ii) placing a 200-microm-wide slit between the sample cell and the detector fibers to mask off the region of weak single scattering and strong multiple scattering from the detectors' field of view, and (iii) aligning the center of the detectors' field of view with the region of strongest single scattering. We analyze a number of suspensions of polystyrene latex spheres with a diameter between 65 and 562 nm in water using this improved one-beam instrument and find that the measured radius is determined in a 2-min data collection time to better than +/-10% for volume fractions of the suspended polystyrene latex spheres up to a few percent.