Metastable states and the kinetics of colloid phase separation

Abstract

Direct visualization of yielding in model two-dimensional colloidal gels subjected to shear flowWe 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 fluidϩcrystal 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 vaporϩliquid binodal hidden in the fluidϩcrystal phase coexistence regime.

Control of protein crystal nucleation around the metastable liquid–liquid phase boundary

“…(ii) The system approaches the spinodal lying below the binodal T L-L (C) (16), similarly to the theoretical predictions for approaches to C crit ,T crit (5,6,8). At the spinodal, (Ѩ 2 ⌬G͞ѨC 2 ) T ϭ 0 (⌬G being the free energy of the solution; ref.…”

“…On further cooling below T crit , the enhancement of nucleation tapers off. Both parts of this prediction have been questioned (7,8). One theory points out that gelation that occurs in a rather broad area around C crit ,T crit (see for instance, ref.…”

“…4) arrests all motion in the solution, and no nucleation enhancement should be expected (7). On the other hand, another set of simulations foresee even faster nucleation in the region of L-L demixing beyond the critical point (8). In view of the practical importance of the protein crystal nucleation and the need for a better understanding of the phase behavior of protein solutions, we set out to study experimentally the nucleation kinetics around the L-L separation boundary.…”

Nonclassical pathways of crystallization in colloidal systems

“…These droplets are usually formed due to the presence of a metastable phase separation [36][37][38]. In colloidal systems, the process has been studied both experimentally [39,40], and theoretically [35,[41][42][43][44]. The number and variety of solutions that have been found to crystallize from dense liquid precursors lead to the idea that two-step crystallization pathways are quite universal crystallization processes.…”

Crystal nucleation as the ordering of multiple order parameters

“…The main theoretical tool for the study of crystallization in simple model systems are density functional theory (DFT) [92,93] and molecular simulations [2,94,95]. Two-step crystallization pathways have been suggested to occur also outside the region of stability of the dense fluid phase.…”