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Open AccessArticle

Thermodynamics of Gas–Liquid Colloidal Equilibrium States: Hetero-Phase Fluctuations

Department of Physics, University of Algarve, 8005-139 Faro, Portugal
Entropy 2019, 21(12), 1189; https://doi.org/10.3390/e21121189
Received: 31 October 2019 / Revised: 25 November 2019 / Accepted: 28 November 2019 / Published: 3 December 2019
(This article belongs to the Special Issue Selected Papers from 15th Joint European Thermodynamics Conference)
Following on from two previous JETC (Joint European Thermodynamics Conference) presentations, we present a preliminary report of further advances towards the thermodynamic description of critical behavior and a supercritical gas-liquid coexistence with a supercritical fluid mesophase defined by percolation loci. The experimental data along supercritical constant temperature isotherms (T > Tc) are consistent with the existence of a two-state mesophase, with constant change in pressure with density, rigidity, (dp/d) T, and linear thermodynamic state-functions of density. The supercritical mesophase is bounded by 3rd-order phase transitions at percolation thresholds. Here we present the evidence that these percolation transitions of both gaseous and liquid states along any isotherm are preceded by pre-percolation hetero-phase fluctuations that can explain the thermodynamic properties in the mesophase and its vicinity. Hetero-phase fluctuations give rise to one-component colloidal-dispersion states; a single Gibbs phase retaining 2 degrees of freedom in which both gas and liquid states with different densities percolate the phase volume. In order to describe the thermodynamic properties of two-state critical and supercritical coexistence, we introduce the concept of a hypothetical homo-phase of both gas and liquid, defined as extrapolated equilibrium states in the pre-percolation vicinity, with the hetero-phase fractions subtracted. We observe that there can be no difference in chemical potential between homo-phase liquid and gaseous states along the critical isotherm in mid-critical isochoric experiments when the meniscus disappears at T = Tc. For T > Tc, thermodynamic states comprise equal mole fractions of the homo-phase gas and liquid, both percolating the total phase volume, at the same temperature, pressure, and with a uniform chemical potential, stabilised by a positive finite interfacial surface tension.
Keywords: hetero-phase fluctuation; percolation transition; supercritical mesophase; liquid state; argon hetero-phase fluctuation; percolation transition; supercritical mesophase; liquid state; argon
MDPI and ACS Style

Woodcock, L.V. Thermodynamics of Gas–Liquid Colloidal Equilibrium States: Hetero-Phase Fluctuations. Entropy 2019, 21, 1189.

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