Transient behavior and time lags in binary nucleation

摘要

To investigate transient binary nucleation, both qualitatively and quantitatively, we numerically solved the birth-death equations for vapor-to-liquid phase transitions. We found that in its early transient stages, binary nucleation rarely, if ever, occurs via the saddle point. Instead most binary systems pass through a temporary stage in which the region of maximum flux extends over a ridge on the free energy surface before reaching the state of saddle point nucleation. Both the number of particles formed and their composition may be affected, and this could be very important for nucleation in glasses and other condensed mixtures for which timescales are very long. In order to plan experiments, accurate estimates of the time lag are important. We therefore directly calculated the time lag for the saddle point flux using our numerical results and compared it with the available analytical predictions. Although the analytical results over-estimate the time lag by factors of 2-6, the numerical results followed the predicted analytical trends quite closely under most conditions.