Free-energy landscape of nucleation with an intermediate metastable phase studied using capillarity approximation

TL;DR

This paper uses capillarity approximation to analyze the free-energy landscape of nucleation involving an intermediate metastable phase, revealing complex nucleation pathways and critical nuclei structures.

Contribution

It introduces a model for nucleation with an intermediate metastable phase, predicting various critical nucleus structures and elucidating nucleation pathways.

Findings

Existence of composite critical nuclei with solid core and liquid layer.

Nucleation can proceed via intermediate metastable liquid phase.

The free-energy landscape reveals multiple nucleation scenarios.

Abstract

Capillarity approximation is used to study the free-energy landscape of nucleation when an intermediate metastable phase exists. The critical nucleus that corresponds to the saddle point of the free-energy landscape as well as the whole free-energy landscape can be studied using this capillarity approximation, and various scenarios of nucleation and growth can be elucidated. In this study we consider a model in which a stable solid phase nucleates within a metastable vapor phase when an intermediate metastable liquid phase exists. We predict that a composite critical nucleus that consists of a solid core and a liquid wetting layer as well as pure liquid and pure solid critical nuclei can exist depending not only on the supersaturation of the liquid phase relative to that of the vapor phase but also on the wetting behavior of the liquid surrounding the solid. The existence of liquid critical nucleus indicates that the phase transformation from metastable vapor to stable solid occurs via the intermediate metastable liquid phase, which is quite similar to the scenario of nucleation observed in proteins and colloidal systems. By studying the minimum-free-energy path on the free-energy landscape, we can study the evolution of the composition of solid and liquid within nuclei not limited to the critical nucleus.