Metastability and spinodals in the lattice gas model

The droplet model of condensation as developed by Fisher (see Physics, vol.3, p.255 (1967)) is modified to take account of: (a) ramified clusters whose surface/volume ratio tends to a finite limit as the number n of constituent molecules becomes large; (b) the excluded volume interactions between clusters. It is found that the interactions change the position of the first singularity in the activity series so that it no longer coincides with the phase boundary but is located beyond it. A thermodynamic metastable state can then be defined as in the classical Gibbs picture.