Colloidal aggregation in the presence of a gravitational field

We present the results of a computational model for colloidal aggregation that considers the Brownian motion, sedimentation and deposition experienced by the colloidal particles and clusters. Among our results, we find that for intermediate strengths of downward gravitational drift, the aggregation crosses over from diffusion-limited colloidal aggregation to another type of aggregation with a higher cluster fractal dimension, D-t. We also get a critical gelation concentration that is higher by several orders of magnitude than for the nondrifting case. We also found a speeding up Followed by a slowing down of the aggregation rate and an algebraically decaying cluster size distribution. As the drift strength becomes much higher, the new fractal dimension is reduced due to the anisotropy of the clusters, becoming more elongated along the vertical direction. We finally present the scaling shown by the cluster size distribution for all the drift strengths studied.