Structural characteristics of sheared suspensions of hydrated colloids
The mass and size frequencies of aggregates formed under low shear by encounters between hydrated colloids of micrometric size was investigated under marginal stability conditions. The mass c(n) and size c(d) frequency curves were determined by particle counting and laser diffractometry, respectively. Correlation between reduced mass and size distributions unequivocally led to the fractal dimension of the aggregates. Aggregation/fragmentation under low shear rate gave rise to aggregates of relatively low fractal dimension when compared to situations of high shear rates. Under marginal stability conditions, the particle concentration and ionic strength differently induced the aggregate formation. In 0.15 M NaCl suspension, aging effects were determined above a threshold concentration while in 0.075 M NaCl suspension, aging effects were observed at all concentrations. Aggregation/fragmentation in 0.15 M NaCl suspensions led to aggregates of fractal dimension 1.4 while in 0.075 M NaCl suspensions, aging and restructuration led to aggregates of fractal dimension 1.8. These relatively low values of the fractal dimension were interpreted by the existence of a preferential orientation of the aggregates in the low shear flow.
Key wordsOrthokinetic aggregation aggregate mass distribution aggregate size distribution hydrated colloids aggregation in a Couette system aggregate fractal dimension
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