Liquid liquid phase transitions: a generalized van der Waals theory
Abstract Book of the XXIII IUPAP International Conference on Statistical Physics, Genova, Italy, (9-13 July 2007)Abstract
Despite the growing interest to the possible polimorphic phase transitions inliquids and glasses (see, for example, for the recent reviews 1) the nature of different phases which can be found in dense (and possibly metastable) liquids is still puzzling. In recent years experimental evidences of such features of phase diagram as liquid-liquid transitions, polyamorphism, etc appeared for a wide range of systems including water, Si, I, Se, S, C, P, etc 1. The complexity of the phase diagrams in these substances may be a result of complex interactions depending on the intermolecular orientations. At the same time exploring the possibility that simple fluids interacting through isotropic potentials may exibit the similar behavior represent a serious challenge for theorists.\newline
The possibility of the existence of a liquid-liquid phase transition drastically depends on the shape of the interparticle potential. Recently, it was shown that the purely repulsive step potential 2 is sufficient to explane a liquid-liquid phase transition. The repulsive step potential is a potential which in addition to the hard sphere core has a repulsive soft core of a larger radius.\newline
Note that the second phase transition, corresponding to the liquid-gas transformation, appears when tail is appended to the repulsive step potential 3. In this talk in the framework of the thermodynamic perturbation theory for fluids we show how the phase diagram of a system of particles interacting through an isotropic potential with an attractive well and a repulsive component consisting of a hard core plus a finite shoulder, where a liquid-liquid phase transition exists in addition to the standard gas-liquid phase transition, changes by varying the parameters of the potential. We show that existence of the liquid-liquid transition is determined by the interplay of the parameters of the potential and the structure of a reference liquid. We also discuss the application of the generalized van der Waals theory to more realistic potentials. \newline
It is necessary to emphasize that liquid-liquid transition is metastable with respect to freezing for all considered parameters.
The work was supported by the Russian Foundation for Basic Research (Grant No 05-02-17280) and NWO-RFBR Grant No 047.016.001
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1) Brazhkin, S.V. Buldyrev, V.N. Ryzhov, and H.E. Stanley eds, New Kinds of Phase Transitions: Transformations in Disordered Substances Proc. NATO Advanced Research Workshop, Volga River (Kluwer, Dordrecht,2002).\newline
2) V.N.Ryzhov, S.M.Stishov Phys.Rev. E 74, 010201 (2003)\newline
3) Yu.D. Fomin, V.N. Ryzhov and E.E. Tareeva Phys. Rev. E 74, 041201 (2006)\newline