COMPARISON OF SIZE AND MORPHOLOGY OF SOOT AGGREGATES AS DETERMINED BY LIGHT-SCATTERING AND ELECTRON-MICROSCOPE ANALYSIS

Soot particles were collected from premixed methane/oxygen flames using a thermophoretic sampling device. Transmission electron micrographs of the soot were optically scanned and stored digitally in a computer. These digitized images where analyzed to determine the mean soot cluster radius of gyration, fractal dimension, number of monomers per cluster, and monomer radius. Effects of three- to two-dimensional projection of the clusters during microphotography were evaluated. These morphological parameters were compared to our recent static light scattering measurements in the same system. In general, good agreement was found for all four parameters. However, monomer number and size from light scattering have a considerable spread due to uncertainties in soot refractive index and a morphological parameter describing the proportionality between monomer number and radius of gyration. We conclude that current theories of fractal cluster scattering and absorption have no egregious errors, but a stringent test could not be made, and that light scattering and mechanical probing yield consistent results.