The mass fractal dimension of aggregates of colloidal polystyrene latex particles was measured using small-angle static light scattering over a range of electrolyte and particle concentrations. The measured fractal dimensions ranged from 1.78 to 2.20, which are in good agreement with the predicted values of the diffusion-limited cluster-cluster aggregation and reaction-limited cluster-cluster aggregation regimes, respectively. It was found that increasing the salt concentration had the effect of reducing the fractal dimension, indicating a more open aggregate structure. Two regimes of behavior were observed for the fractal dimension as a function of particle concentration. At high salt levels (>1 M KNO3) the particle concentration was seen to have little or no effect, while at low salt levels (<1 M KNO3) an increase in concentration led to a decrease in the fractal dimension. This was attributed to a reduction in the time available for reconfiguring of particles in the aggregates due to an increased particle collision frequency. The particle aggregation rate was also found to increase at higher electrolyte levels and with larger particle concentrations.
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|Published - 26 Nov 1997