Direct Observation of Single Ostwald Ripening Processes by Molecular Dynamics Simulation

Abstract

Ostwald ripening is an important growth process in many scientific disciplines ranging from material science, geology, biophysics, and product formulation. Here ripening of argon clusters in a vapor phase is observed directly in constant energy molecular dynamics simulations serving as a model system for large-time scale ripening processes. Starting from an initial metastable equilibrium between the vapor phase and two clusters Ostwald ripening is initiated by the addition of kinetic energy. This mimics local thermal fluctuations in a larger system. It appears that there is not necessarily a close encounter of two clusters before ripening sets in. Also no static density bridge between two ripening clusters is observed. The onset of ripening is rather related to the different evaporation dynamics of clusters of different size. It can start at the moment energy is added or with some delay, depending on the difference in cluster size and dynamics.

Ostwald ripening in multiple-bubble nuclei

“…While a number of experiments on Ostwald ripening have been performed [2][3][4][5][6]11], few have focused on bubble nuclei, especially homogenous nuclei. There have been studies, in which the nuclei of a small numbers of bubbles were numerically simulated by molecular dynamics (MD) simulations [12][13][14][15][16]. However, there have been virtually no studies on the simulation of a multiple-bubble system with sufficient number of bubbles to study Ostwald ripening, mainly due to the lack of computational power.…”

“…However, there have been virtually no studies on the simulation of a multiple-bubble system with sufficient number of bubbles to study Ostwald ripening, mainly due to the lack of computational power. Additionally, bubbles were initiated by hot spots in the past studies [12,14]. Therefore, simulations of homogenous nuclei without initiation has been waiting.…”

Cluster growth mechanisms in Lennard-Jones fluids: A comparison between molecular dynamics and Brownian dynamics simulations

“…Although the diffusion and coalescence of liquid droplets in a vapor phase have been frequently reported in previous MD simulations [8,11,16,17], the observation of the Ostwald ripening from molecular simulations has been rarely reported [15]. Kraska performed MD simulations of a liquid-vapor phase separation of an argon gas and reported the direct observation of the Ostwald ripening in some cases out of several MD trials [15]. By observing the Ostwald ripening in BD simulations starting from an initially homogeneous distribution of self-interacting particles, our work further suggests that the molecular aggregation and cluster growth in a mesoscopic level may proceed via the Ostwald ripening.…”

“…The kinetics of the vapor-liquid phase separation and formation of liquid droplets in LJ fluids that are close to the two-phase boundary have also been intensively studied, particularly, in the short-time regime with a view in understanding the nucleation kinetics [8][9][10][11][12][13][14]. However, until very recently [15][16][17], the kinetics of the droplet formation in the long-time regime has not been reported by molecular simulations.…”

“…It has also been suggested that the Ostwald ripening is one of the main routes in degrading the emulsion stability by coarsening the emulsion droplets [29,30]. Although the diffusion and coalescence of liquid droplets in a vapor phase have been frequently reported in previous MD simulations [8,11,16,17], the observation of the Ostwald ripening from molecular simulations has been rarely reported [15]. Kraska performed MD simulations of a liquid-vapor phase separation of an argon gas and reported the direct observation of the Ostwald ripening in some cases out of several MD trials [15].…”