Kinetic control of competing nuclei in a dimer lattice-gas model

Abstract

Nucleation is a key step in the synthesis of new material from solution. Well-established lattice-gas models can be used to gain insight into the basic physics of nucleation pathways involving a single nucleus type. In many situations a solution is supersaturated with respect to more than one precipitating phase. This can generate a population of both stable and metastable nuclei on similar timescales and hence complex nucleation pathways involving competition between the two. In this study we introduce a lattice-gas model based on two types of interacting dimer representing particles in solution. Each type of dimer nucleates to a specific space-filling structure. Our model is tuned such that stable and metastable phases nucleate on a similar timescale. Either structure may nucleate first, with probability sensitive to the relative rate at which solute is replenished from their respective reservoirs. We calculate these nucleation rates via Forward-Flux Sampling and demonstrate how the resulting data can be used to infer the nucleation outcome and pathway. Possibilities include direct nucleation of the stable phase, domination of long-lived metastable crystallites, and pathways in which the stable phase nucleates only after multiple post-critical nuclei of the metastable phase have appeared.

Interplay of multiple clusters and initial interface positioning for forward flux sampling simulations of crystal nucleation

“…In addition, the shape of the OP distribution may be sensitive to changes in cluster definition, and therefore the mean and the mode may not be coincident and the standard deviation may become significant. While changes in cluster definition may also exacerbate other differences between observed clusters, such as arrangement 38 and polymorph, 39 which may also influence the nucleation rate, this is not always the case.…”

“…This can be very significant in some cases, e.g., when comparing the dominance of two process with closely competing rates, as in Ref. 39.…”

Special Topic Preface: Nucleation—Current understanding approaching 150 years after Gibbs

“…The authors propose a scaling function that reproduces the computed free energies of droplet formation across the full range of metastabilities (binodal to spinodal). Mandal and Quigley 44 present a lattice-gas model involving two types of interacting dimers, revealing complex pathways for the nucleation of stable and metastable phases. The model, tuned for similar nucleation time scales of the stable and metastable phases, yields outcomes ranging from direct stable phase nucleation, dominance of longlived metastable crystallites, to stable phase nucleation after multiple nuclei of the metastable phase appear.…”