We propose a model describing the liquid-vapour phase transition according to a phase-field approach. The model takes up a setting proposed by the second author, where a phase field is introduced whose equilibrium values 0 and 1 are associated to the liquid and vapour phases. The phase field obeys Ginzburg-Landau equation and enters the constitutive relation of the density, accounting for the sudden density jump occurring at the phase transition. In this paper we concern ourselves with the extension of this model to take into account the existence of the critical point in the coexistence line.

15 pages, 4 figures