STRUCTURE OF FRACTAL COLLOIDAL AGGREGATES FROM SMALL ANGLE X-RAY SCATTERING

Abstract
The structure of aggregates of colloidal silica is studied by small angle x-ray scattering. These aggregates have a ramified appearance. The aggregates are appropriately described by fractal geometry and, therefore, by a fractal dimension, D. D is determined from the slope of the static structure factor in the regime KRg >> 1 >> Ka where Rg is an average radius of gyration of the aggregates, a is the radius of the colloidal "monomer" and K is the magnitude of the scattering vector. We find D = 2.0 ± .15. At Ka = 1, a crossover to D = 3 is found, consistent with the dense structure of the colloidal monomer

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