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Chapter II Solution Growth….
pressure of the liquid phase at the same temperature known as equilibrium
pressure P*, the vapor is described as under-saturated, saturated or
supersaturated, respectively with respect to the liquid phase. The under-
saturated state and saturated state are thermodynamically stable. The
supersaturated vapor in contact with the bulk liquid phase will condense into
the liquid until saturation is obtained.
In a supersaturated vapor, not only monomers A1 are present but also
embryos, which are clusters of molecules bound together by their
intermolecular interactions. The mechanisms of formation of such embryos is
the simple collision process consisting of a single molecules A1 with a cluster
Ai-1 consisting of (i-1) molecules and hence giving rise to a cluster Ai as follows
A1 + Ai-1 → Ai
The cluster Ai may also form by the evaporation of a molecule from some
cluster Ai+1 as follows,
Ai+1 → Ai + A1
The phase change takes place by single molecule attached to
embryos of various sizes, this process predominant slightly over the reverse
process in which the different embryos lose single molecules. The size
distribution of embryos changes with time, the numbers of the larger ones
increasing. There is a critical size which is unstable equilibrium with the
supersaturated vapor and this critical nucleus forms the bottleneck of the
phase change. Once embryos achieve this critical size, there is a high
probability that they will grow, relatively unhindered, to microscopic size.
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