INSITU GROWTH AND STRUCTURE OF FRACTAL SILICA AGGREGATES IN A FLAME

We studied flame-generated (fumed) silica particles in situ by static and dynamic light scattering and ex situ by transmission electron microscopy. The growth and aggregation of the particles were followed as a function of height in the flame. The scattered intensity appeared to be consistent with a fractal aggregate structure having a fractal dimension of D equals 1. 49 (smaller than previously reported ex situ measurements of fumed silica) although the data are too limited to determine D with certainty. From the dynamic light scattering results, corrected for polydispersity, the growth trend appeared to deviate from free-molecular behavior for long residence times. From the electron microscopy, we noted a surprising tendency for the silica monomers to shrink with residence time.