Metastable states and the kinetics of colloid phase separation

We report on the results of extensive Brownian dynamics simulations of colloid phase separation due to depletion flocculation. We study in detail the effect of potential variation at fixed volume fraction of colloid and fixed range of interaction. We find a variety of nonequilibrium behaviors for quenches into the colloid fluid+crystal phase coexistence regime. We present clear evidence of metastability, of homogeneous nucleation, and of a kinetically arrested gel state. We also find evidence that suggests a density instability in the metastable colloid fluid preceding crystal nucleation. Our findings are consistent with a previous proposal that nonequilibrium behavior is determined by a metastable vapor+liquid binodal hidden in the fluid+crystal phase coexistence regime. (C) 1999 American Institute of Physics. [S0021-9606(99)51304-4].