Structure factor scaling in colloidal phase separation

PACS number(s): 82.70.Gg, 82.70.RrThe dynamical scaling hypothesis for the structure factor, S(q), in depletion-driven colloidal phase separation is studied by carrying out Brownian dynamics simulations. A true dynamical scaling is observed for shallow quenches into the two-phase coexistence region. In such a quench, compact clusters nucleate and grow with time and there is only one characteristic length scale in the system after an initial transient period. Scaling is satisfied beyond this initial period. In contrast, deep quenches lead to fractal cluster growth, and the system is controlled by two characteristic lengths that evolve differently in time [ Huang, Oh and Sorensen Phys. Rev. E 57 875 (1998)]. True dynamical scaling thus cannot be expected to hold. However, an apparent scaling for the structure factor is observed over some period of time when these two characteristic length scales become comparable to each other. We compare our simulation results for the total structure factor to theoretical predictions by HOS by writing it as a product of cluster-cluster and the averaged single-cluster structure factors, each with its own characteristic length.J.J.C. and T.S. acknowledge financial support from the Spanish MCyT Grant No. BMF2001-0341-C02-01. A.C. and C.S. are supported by NASA Grant No. NNC04GA74GPeer reviewe