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 $S(q)$, in the 3D simulations of diffusion-limited colloid aggregation. We unambiguously identify the peak in $S(q)$ as arising from the correlation between particles belonging to nearest-neighbor clusters. The $S(q)$ 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 $S(q)$ from the simulations of reaction-limited colloid aggregation is also found.