Generalized Kelvin equation and pseudospinodal in nucleation theory

The classical Kelvin equation, relating the size of the critical cluster to the supersaturation, is inadequate for very small, molecular-sized clusters emerging at deep quenches observed in recent nucleation experiments. Using statistical mechanical considerations, we propose a generalization of the Kelvin equation applicable up to the vicinity of the pseudospinodal, where the nucleation barrier is approximately k(B)T. The supersaturation at the pseudospinodal is expressed in terms of the second virial coefficient. It is shown that near the pseudospinodal the critical cluster size is close to the coordination number in the liquid phase. Comparisons with computer simulations are presented.