Phase diagram versus diagram of solubility: What is the difference for nanosystems?

Particles with diameters in the range of 1–100 nm are characterized by the fact that the ratio of the number of surface to volume atoms is not small. It is then obvious that the effects of the surface on the cohesive properties of the particle cannot be neglected. In particular, the equilibrium phase diagram of nanoparticles differs from the corresponding bulk one. It is size dependent. Moreover, it is argued here that, in nanosystems, the concept of equilibrium phase diagram has to be revised. It turns out that it is required to differentiate the solidus and liquidus curves and equilibrium curves after the first order phase transition for a nanosystem. The new notions of ‘solubility diagram’, ‘solidus’, ‘liquidus’, and ‘nanophase diagram’ outlined here provide an acceptable description of the phase transition phenomenon in a nanosystem.