Determination of the Equivalent Radii and Fractal Dimension of Polystyrene Latex Aggregates from Sedimentation Coefficients

Abstract

Sedimentation coefficients of small polystyrene latex aggregates (n= 2, 3, 4) were determined by centrifugation of a coagulated latex sample within a density gradient and fitted to theR* =ncrequation, whereR* is the equivalent radius of the aggregate,ris the radius of each individual sphere, andc= 0.58. This equation was also satisfactorily used to fit latex aggregate diffusion data, previously published by other authors. The constantcagrees with the value calculated from the fractal dimensionDfreported for larger aggregates in the literature, usingc= 1/Df. As a conclusion, aggregate sedimentation and diffusion coefficients can be obtained from light-scattering and microscopical data, and vice versa, using a scaling factor which is related to the aggregate fractal dimension.