Clustering of non-bonded molecules has long been recognised in the thermodynamic description of gases and dilute solutions. Recently [1], space-spanning networks of non-bonded molecular clusters, percolation effects, were identified as second-order thermodynamic phase transitions. Simulation studies have resulted in novel description of critical phenomena and the discovery of supercritical phase regions [2] and a thermodynamic description of gas-liquid criticality, that is quite different from  van der Waals hypothesis.At Tc , in the density (p,T) surface, there is no critical point. Using tabulations of p-V-T data, for supercritical argon, and also water and steam, as examples, at Tc , liquid and vapor phases, determined by percolation transition densities, coexist. At Tc, there is a line of critical coexistence states of constant chemical potential at the intersection of two percolation loci in the p-T plane. For temperatures above this line, there are three supercritical fluid phases characterised as follows: (i) gas phase with distribution of small finite clusters (ii) a homogeneous mesophase, but, with both small finite clusters and system-spanning clusters, and (iii) the supercritical liquid phase with just one cluster.[1] Leslie V. Woodcock, �Thermodynamic description of liquid state limits�, ACS J. Phys. Chem. B 2012, 116, 3735-3744 (2012)[2] Leslie V. Woodcock, �Observations of a thermodynamic liquid�gas critical coexistence line and supercritical fluid phase bounds from percolation transition loci�, Fluid Phase Equilibria (2012), http://dx.doi.org/10.1016/j.fluid.2012.08.029

Percolation transitions of non-bonding clusters: A critical coexistence and a supercritical mesophase

245th National Meeting (2013)

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