  In patchy particle systems where there is competition between the
self-assembly of finite clusters and liquid-vapour phase separation, reentrant
phase behaviour is observed, with the system passing from a monomeric vapour
phase to a region of liquid-vapour phase coexistence and then to a vapour phase
of clusters as the temperature is decreased at constant density. Here, we
present a classical statistical mechanical approach to the determination of the
complete phase diagram of such a system. We model the system as a van der Waals
fluid, but one where the monomers can assemble into monodisperse clusters that
have no attractive interactions with any of the other species. The resulting
phase diagrams show a clear region of reentrance. However, for the most
physically reasonable parameter values of the model, this behaviour is
restricted to a certain range of density, with phase separation still
persisting at high densities.
