THE EFFECT OF POLYDISPERSITY IN PRIMARY PARTICLE-SIZE ON MEASUREMENT OF THE FRACTAL DIMENSION OF AGGREGATES

The use of the mass fractal dimension has become a popular method of c haracterising the structure of aggregates of fine particles. This para meter is often inferred from scattering experiments that exhibit a pow er law con-elation between scattered intensity and the scattering vect or. In this paper we demonstrate deviations from this behaviour that o ccur when the particles making up the aggregate are not monodisperse, even though the aggregate maintains the same fractal structure as obse rved in the monodisperse case. We have performed light scattering expe riments with aggregating colloidal haematite and performed DLCA comput er simulations to explain the observed behaviour. The behaviour can in fluence the determination of the mass fractal dimension, as can other factors such as scattering effects from primary particles.