Light scattering studies on a coagulating polystyrene latex

Abstract

The changes occurring in the angular distribution of scattered light during the rapid coagulation of a polystyrene latex (diam. 126 nm) have been measured at two wavelengths for times up to the half-life, and compared with those calculated from theory in which the number concentration of the aggregates are taken to be those given by von Smoluchowski's second-order kinetics and in which the scattering properties of aggregates are described in terms of optical interference between their constituent primary particles. The agreement was good but absolute intensity measurements on the initial latex dispersion differed from those calculated from the Mie theory in a manner indicative of partial aggregation. When this was taken into account, excellent agreement between the measured and calculated angular distributions was obtained at all angles between 30 and 135° at both wave-lengths for times up to the half-life. The absolute rate constant for rapid coagulation was 67-69 % of the theoretical Smoluchowski value.