Particle Size Distribution Measurements of PolymericDispersions: A Comparative Study

Abstract

Average particle sizes and particle size distributions (PSD) were measured using four different commercial techniques for standard polystyrene latexes in the submicron range, dynamic light scattering (DLS), capillary hydrodynamic fractionation (CHDF), disk centrifuge photosedimentometry (DCP) and transmission electron microscope (TEM). Both monodisperse latexes and broad particle size distribution latexes (obtained by mixing two or three monodisperse standards) were used in each equipment. It was found that for monodisperse latexes, DLS, CHDF and DCP gave similar measurements of particle size, which were also comparable to the particle sizes measured by TEM and reported by the supplier of the standard latexes. However, with the lowest particle size standard (39 nm), both DLS and CHDF gave larger particle size values, whereas with DCP, reasonable agreement with the measured size was obtained only when extremely long centrifugation times (at least 6 h) were used. For latexes having bimodal and trimodal distributions, both CHDF and DCP were able to reproduce the entire distribution, providing relatively accurate values for the average size of each mode and also the relative masses of each population of particles. However, the analysis time required by CHDF was shorter than by DCP, but the broadness of the peak was better captured by DCP than CHDF, which always provided broader peaks. DLS failed in most cases when measuring the broad size populations when the size ratio was greater than 2 : 1.