Spatial Ordering and Structure Factor Scaling in the Simulations of Colloid Aggregation

We report the observation of spatial ordering of clusters that leads to a spinodal-type scaling of the structure factor $S\left(q\right)\mathrm{}$, in the 3D simulations of diffusion-limited colloid aggregation. We unambiguously identify the peak in $S\left(q\right)\mathrm{}$ as arising from the correlation between particles belonging to nearest-neighbor clusters. The $S\left(q\right)\mathrm{}$ has a terminal shape that corresponds to a close packing of the clusters after gelation, in a concentration range larger than the one suggested in recent experiments. A finite-$q$ peak in $S\left(q\right)\mathrm{}$ from the simulations of reaction-limited colloid aggregation is also found.