A simple g(E)-model for generating all basic types of binary liquid-liquidequilibria and their pressure dependence. Thermodynamic constraints at critical loci

We survey the types of binary (T,p,x) liquid-liquid phase diagrams that hav e already been found experimentally or that can be predicted to exist, emph asizing the topological properties of the temperature-pressure relation alo ng their critical loci. We use the simplest g(E)-model compatible with all known basic behavior. The distinct types of phase diagrams are also discuss ed in light of simple molecular arguments. These, in turn, will serve to pr edict the thermodynamics of the mixture, i.e., the underlying excess enthal pic, entropic, and volumetric properties to which the g(E)-model has to con form. The temperature and pressure dependences of these thermodynamic quant ities play a fundamental role. From this functional point of view, all poss ible (T,p,x) phase diagrams can be reduced to just four types. The model pr esents six parameters with direct physical meaning. While the slope of the T-p curve for critical demixing permits us to establish a relation between h(E) and v(E), its curvature enables us to obtain information about the mix ture's compressibility and heat capacity as well. The last section is devot ed to the analysis of more complicated cases than those corresponding to ba sic types of phase diagrams.