Abstract
Critical phenomena in real fluids demonstrate a combination of universal features caused by the divergence of long-range fluctuations of density and nonuniversal (system-dependent) features associated with specific intermolecular interactions. Asymptotically, all fluids belong to the Ising-model class of universality. The asymptotic power laws for the thermodynamic properties are described by two independent universal critical exponents and by two independent nonuniversal critical amplitudes; other critical amplitudes can be obtained by universal relations. The nonuniversal critical parameters (critical temperature, pressure, and density) can be absorbed in the property units. Nonasymptotic critical behavior of fluids can be divided into two parts, symmetric ("Ising-like") and asymmetric ("fluid-like"). The symmetric nonasymptotic behavior contains a new universal exponent (Wegner exponent) and the system-dependent crossover scale (Ginzburg number) associated with the range of intermolecular interactions, while the asymmetric features are generally described by an additional universal exponent and by three nonasymptotic amplitudes associated with mixing of the physical fields into the scaling fields.
Highlights
Universality of critical phenomena is one of the most fascinating concepts in physics of condensed matter [1, 2] Phase transitions of strikingly different nature, such as para-ferro-magnetism, vaporization, or fluid demixing may be described by the same equation of state near the critical points if a proper (“isomorphic”) set of thermodynamic variables is chosen
The order parameter in fluids is associated with the density or concentration while the order parameter in anisotropic magnetics is a one-component vector
This theory of asymmetric fluid criticality is an extension of the field-mixing in a revised scaling and incorporates the hypothesis of Griffiths and Wheeler [43] that preferable thermodynamic variables do not exist
Summary
Universality of critical phenomena is one of the most fascinating concepts in physics of condensed matter [1, 2] Phase transitions of strikingly different nature, such as para-ferro-magnetism, vaporization, or fluid demixing may be described by the same equation of state near the critical points if a proper (“isomorphic”) set of thermodynamic variables is chosen. This particular nature of the order parameter affects the phase-transition dynamics It is well established, primarily through experiments [3, 4], that all fluids and fluid mixtures belong to the Ising-model class of universality in statics and to the conserved-order-parameter class of universality in dynamics. Primarily through experiments [3, 4], that all fluids and fluid mixtures belong to the Ising-model class of universality in statics and to the conserved-order-parameter class of universality in dynamics This universality is associated with the universal nature of critical fluctuations. The critical temperature ranges from a few kelvins for helium isotopes to thousands of kelvins for liquid metals This particular non-universal feature can be eliminated by reducing the properties of a particular substance by its critical parameters. I present a brief overview of universal and nonuniversal contributions to the equation of sate of near-critical fluids
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