Light Scattering Study of Aggregation Kinetics in Dense, Gelling Aerosols

Abstract

We report the results of a study of the kinetics of a dense aggregating aerosol system that show that the predictions of the Diffusion Limited Cluster Aggregation (DLCA) model no longer hold when the system is dense. We studied a soot aerosol using the small angle light scattering technique created by exploding a mixture of a hydrocarbon gas and oxygen in a closed chamber. The soot particles started as individual monomers, ca. 38 nm radius, grew to bigger fractal clusters with time and finally stopped evolving after spanning a network across the whole system volume. This spanning is aerosol gelation. The study of the kinetics of the aggregating system showed that as the system evolved from a cluster dilute to cluster dense system, the aggregation kernel homogeneity λ evolved from the dilute limit, DLCA value of zero to a value 0.42 +/− 0.05 at the gel point. This evolution is consistent with previous simulation and theory. The experimental value at the gel point is nearly equal to the value of 0.5 predicted by simulation and theory. In addition, the magnitude of the aggregation kernel showed an increase with increasing volume fraction.