Latex Particle Size Distribution by Dynamic Light Scattering. A New Data Processing for Multiangle Measurements

Abstract

Multi-angle dynamic light scattering (DLS) provides a better estimate of the particle size distribution (PSD) than single-angle DLS. However, multi-angle data treatment requires to appropriately weight each autocorrelation measurement prior to calculating the PSD. The weighting coefficients may be directly obtained from: i) the autocorrelation baselines, or ii) independent measurement of the average light intensity by elastic light scattering. However, the propagation of errors associated to such procedures may intolerably corrupt the PSD estimate. In this work, an alternative recursive least squares calculation is proposed that estimates the weighting coefficients on the basis of the complete autocorrelation measurement. The method was validated through a numerical example that simulates the analysis of a polystyrene latex with a bimodal PSD; and with “measurements” taken at 10 detection angles. The ill-conditioned nature of the problem determines that the “true” PSD cannot be recuperated, even in the absence of errors. A sensitivity analysis was carried out to determine the effect of errors in the weighting coefficients on the PSD recuperations.