Three-phase fractionation of polydisperse fluids

It is shown that the van der Waals free-energy of polydisperse fluids, as introduced previously (L. Bellier-Castella, H. Xu and M. Baus, {J. Chem. Phys.} {113}, 8337 (2000)), predicts that for certain thermodynamic states (e.g. low temperatures and large polydispersities) the ordinary two-phase coexistences become metastable relative to a fractionation of the system into three phases, reducing thereby the polydispersity of each of the coexisting phases.