Colloidal aggregation with sedimentation: computer simulations.

A computer model for colloidal aggregation is presented that considers both the Brownian motion and the gravitational drift experienced by the colloidal particles and clusters. It is shown that the aggregation crosses over from diffusion-limited aggregation to another type with a higher cluster fractal dimension, a speeding up followed by a slowing down of the aggregation rate, an algebraically decaying cluster size distribution, and a higher concentration required for gelation. Although these findings are in accordance with the experimental results, some interpretations are different.