Key words: critical point, crossover theory, supercritical fluids, scaling, equation of state, Widom lines
This review provides a detailed description of the main provisions of the modern non-classical theory of critical phenomena in pure fluids, based on the hypothesis of scale invariance (scaling). The main types (parametric and six-term or renormalized Landau expansion), theoretically based, crossover equations of state (EoS) of pure fluids and their application to describe the anomalous behavior of thermodynamic properties near and supercritical fluids are described in detail. It is shown that the crossover model of EoS covers all the characteristic features of the scaling behavior of the thermodynamic properties of pure fluids in the asymptotic region of the critical point (CP) in the form of simple power laws with universal critical exponents and transforms into the classical EoS (in particular, the Landau expansion) far from the critical (fluctuation) region. A detailed comparison of the predictions of the crossover model of EoS with experimental data on thermodynamic properties for a wide class of supercritical fluids in a wide range of temperatures and pressures is presented. Crossover EoS of pure fluids were used to quantify the boundary of the region ofinfluence of critical fluctuations on thermodynamic properties, i.e., to estimate the contribution of the fluctuation component to the experimentally observed anomalous of the thermodynamic properties of supercritical fluids. An interpretation of supercritical phase transitions (Widom lines) is given on the basis of the concept of large-scale critical fluctuations and the crossover theory. The review also considers dynamic crossover phenomena to describe the effect of fluctuations on the critical increase in transport properties (thermal conductivity, conductivity temperature, and viscosity) near and in supercritical fluids.
doi:10.1134/S1990793124700970