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Crossover dynamics at large metastability in gas-liquid nucleation
Phys. Rev. E 83, 031602 – Published 17 March, 2011
DOI: https://doi.org/10.1103/PhysRevE.83.031602
Abstract
We have developed an alternate description of dynamics of nucleation in terms of an extended set of order parameters. The order parameters consist of an ordered set of th largest clusters, ordered such that 1 is the largest cluster in the system, 2 is the second largest cluster, and so on. We have derived an analytic expression for the free energy for the th largest cluster, which is in excellent agreement with the simulated results. At large supersaturation, the free energy barrier for the growth of the th largest cluster disappears and the nucleation becomes barrierless. The major success of this extended theoretical formalism is that it can clearly explain the observed change in mechanism at large metastability [P. Bhimalapuram et al., Phys. Rev. Lett. 98, 206104 (2007)] and the associated dynamical crossover. The classical nucleation theory cannot explain this crossover. The crossover from activated to barrierless nucleation is found to occur at a supersaturation where multiple clusters cross the critical size. We attribute the crossover as the onset of the kinetic spinodal. We have derived an expression for the rate of nucleation in the barrierless regime by modeling growth as diffusion on the free energy surface of the largest cluster. The model reproduces the slower increase in the rate of growth as a function of supersaturation, as observed in experiments.
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