Multiple critical points and liquid–liquid equilibria from the van der Waals like equations ofstate

Abstract

The principal aim of this work is a comprehensive analysis of the phase diagram of watervia the van der Waals like equations of state (EoSs) which are considered as superpositionsof repulsive and attractive forces. We test more extensively the modified van der Waals EoS(MVDW) proposed by Skibinski et al (2004 Phys. Rev. E 69 061206) and refine this modelby introducing instead of the classical van der Waals repulsive term a very accuratehard sphere EoS over the entire stable and metastable regions (Liu 2006 Preprintcond-mat/0605392). It was detected that the simplest form of MVDW EoS displays acomplex phase behavior, including three critical points, and identifies four fluid phases(gas, low density liquid (LDL), high density liquid (HDL), and very high density liquid(VHDL)). Moreover the experimentally observed (Mallamace et al 2007 Proc. Natl Acad.Sci. USA 104 18387) anomalous behavior of the density of water in the deeplysupercooled region (a density minimum) is reproduced by the MWDW EoS. Animprovement of the repulsive part does not change the topological picture of thephase behavior of water in the wide range of thermodynamic variables. The newparameters set for second and third critical points are recognized by thorough analysisof experimental data for the loci of thermodynamic response function extrema.