Global asymmetry of fluids and local singularity in the diameter of the coexistence curve

Abstract

By combining a measurable vapor-liquid coexistence curve and the extended van der Waals-type of equation of state (EOS) with the additional temperature-dependent coefficient, the phenomenological model of global fluid asymmetry has been developed separately for both coexisting bulk phases in the entire range of subcritical states. It is shown, in particular, that the adequate description of a liquid branch and its near-critical vicinity in terms of appropriate critical exponents and amplitudes connected by the two-scale-factor universal interrelations can be achieved. The asymmetric influence of heterophase fluctuations on the criticality of gaseous states is demonstrated. It is inherently similar to the well-known Fisher's droplet model, which corresponds to the scaling EOS too. The principle of corresponding isotherms has been formulated without any adjustable parameters. An attempt to avoid the use of a locally singular coexistence-curve diameter is proposed in the framework of two alternative models. The accurate vapor-liquid data for two fluid metals, Rb and Cs, as well as two molecular fluids, C(2)H(6) and CO(2), are reanalyzed by the above models to confirm the presumed opportunity.

Scaling Model of Low-Temperature Transport Properties for Molecular and Ionic Liquids

“…It was shown recently [2,3] in the framework of FTmodel [4][5][6] that the aforementioned oversimplifications of ss-and/or hs-model are not necessary if one considers the more realistic LJ-type potential , / with the effectivedependent parameters ( ), ( ): The advantage of such approach in comparison with the conventional estimates of their constant LJ-counterparts , (mainly, from the experimental second-virial-coefficient's data) follows from the exact -dependence derived by FTmodel for any subcritical temperature:…”

“…Asymmetry between the Nonordered (Gas) and Condensed (Liquid) States FT-model is described in detail elsewhere [2,6]. For the convenience of readers its main concepts and results are discussed, in brief, below.…”

“…The choice here of LJ-form requires, for information, at least, the superficial comparison of FT-model's results with the enormous number of simulated LJ-data described [8] just by the unified, purely empirical (so-called, fundamental) EOS for free energy. Despite the widespread belief of its universal applicability the arguments in favor of global indubitable asymmetry between -and -states [2] are represented below in terms of respective local thermal EOSs. Another theoretical consequence of the discussed duality is the necessity to modify significantly the description of transport coefficients (see Section 3) without the permanent appeals to the well-established PCS formalism of a diluted nonordered -phase and its properties [9,10].…”

“…Another notable feature here is the implied PCS (principle of corresponding states) nature of such ss-scaling. Indeed one has to fix the exponent in (1) and (2) to select the group of similar substances.…”

“…Nevertheless the useful consequence of scaling transformation has been noticed by Hoover et al [1] because any equilibrium or transport reduced properties (e.g., dynamic viscosity −2/3 ( 0 ) −1/2 or self-diffusion 1/3 ( 0 / ) 1/2 , 0 mass of particle) of different ss-systems with fixed exponent should coincide at the different and being expressed in terms of -variable from (2). Of course, the additional serious restriction of ss-model (common with hs-model) is an absence of gas-(vapor-) liquid ( , ) transition at any value of repulsive exponent.…”