Dynamic light scattering of dispersed fumed silica aggregates

The characterisation of particle aggregates with dynamic light scattering yields an effective hydrodynamic diameter, which is dependent on the scattering angle. This dependency is partly due to polydispersity, but mainly caused by the aggregates’ rotational diffusion. The paper examines this effect of rotation for suspensions of fumed silica by means of static and dynamic light scattering. A universal relationship between the hydrodynamic diameter and scattering angle was sought, as predicted by theory for DLCA aggregates (i.e. formed by diffusion limited cluster aggregation). The employed suspensions differed in BET of the powder (i.e. primary particle size) and state of dispersion.