Determination of the equivalent radii and fractal dimension of polystyrene latex aggregates from sedimentation coefficients

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 the R* = n(c)r equation, where R* is the equivalent radius of the aggregate, r is the radius of each individual sphere, and c = 0.58. This equation was also satisfactorily used to fit latex aggregate diffusion data, previously published by other authors. The constant c agrees with the value calculated from the fractal dimension D-f reported for larger aggregates in the literature, using c = 1/D-f. 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. (C) 1998 Academic Press.