Transition from nucleation and growth to Ostwald ripening

Abstract

Condensation phase transitions from metastable fluids occur by nucleation with accompanying cluster growth and eventual Ostwald ripening. In closed batch systems the supersaturation declines as clusters nucleate and grow, causing an increase in the stable critical nucleus size. During ripening the subcritical clusters are considered to dissolve spontaneously, so that their mass is released to contribute to further growth of remaining clusters. A model based on the dynamics of cluster size distributions (CSDs) represents this sequence of phenomena in terms of four-dimensionless parameters: initial supersaturation, power on the cluster-mass expression for the growth rate coefficient, and parameters for nucleation rate and Gibbs–Thomson effect. A numerical solution of the scaled governing equations for CSD and supersaturation shows the transition from nucleation and growth to ripening, which can occur over a relatively long time period, thus separating the stages. The asymptotic ripening stage shows a power law increase in average cluster mass as the CSD evolves to (minimum) polydispersity index of unity.