Absolute Heteroaggregation Rate Constants by Multiangle Static and Dynamic Light Scattering

Abstract

The analysis of early-stage heteroaggregation (or heterocoagulation) in binary colloidal systems composed of oppositely charged latex particles of different size in the submicrometer size range with multiangle static and dynamic light scattering is presented. The solution conditions were adjusted to exclude any significant homoaggregation. The apparent rate obtained from static light scattering mostly strongly decreases with increasing scattering angle regardless of the number fractions, while the rate from dynamic light scattering varies in a more complicated manner. The light scattering data could be interpreted quantitatively on the basis of the Rayleigh−Gans−Debye approximation. The values of absolute heteroaggregation rate constants were found to be the same within experimental error when evaluated from static or dynamic light scattering, and they were independent of the mixing ratio. The average hydrodynamic radius of the doublet obtained from the dynamic light scattering was in good agreement with theoretical estimates based on an exact hydrodynamic treatment at low Reynolds numbers. A simple formula is proposed to estimate the hydrodynamic radius of the asymmetric particle doublet, and this formula is shown to agree well with experimental data and with theory. The new conclusion from this study is that multiangle dynamic light scattering represents the method of choice for the determination of absolute heteroaggregation rate constants.