The Frenkel Line: a direct experimental evidence for the new thermodynamic boundary

Abstract

Supercritical fluids play a significant role in elucidating fundamental aspects of liquid matter under extreme conditions. They have been extensively studied at pressures and temperatures relevant to various industrial applications. However, much less is known about the structural behaviour of supercritical fluids and no structural crossovers have been observed in static compression experiments in any temperature and pressure ranges beyond the critical point. The structure of supercritical state is currently perceived to be uniform everywhere on the pressure-temperature phase diagram, and to change only in a monotonic way even moving around the critical point, not only along isotherms or isobars. Conversely, we observe structural crossovers for the first time in a deeply supercritical sample through diffraction measurements in a diamond anvil cell and discover a new thermodynamic boundary on the pressure-temperature diagram. We explain the existence of these crossovers in the framework of the phonon theory of liquids using molecular dynamics simulations. The obtained results are of prime importance since it implies a global reconsideration of the mere essence of the supercritical phase. Furthermore, this discovery may pave the way to new unexpected applications and to the exploration of exotic behaviour of confined fluids relevant to geo- and planetary sciences.

11 pages, 5 figures

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• Thermodynamic crossovers in supercritical fluids
• Universality, scaling and collapse in supercritical fluids
• "Two-phase" thermodynamics of the Frenkel line
• Some Early Ideas on the Metric Geometry of Thermodynamics
• Topological generalization of the rigid-nonrigid transition in soft-sphere and hard-sphere fluids
• Standing shock prevents propagation of sparks in supersonic explosive flows
• Dynamical and thermodynamic crossovers in the supercritical region of a holographic superfluid model
• Mesoscopic Collective Dynamics in Liquids and the Dual Model
• The Viscosity of Liquids in the Dual Model
• Formation of Argon Cluster with Proton Seeding
• Revisiting the question of what instantaneous normal modes tell us about liquid dynamics
• The Frenkel line and the pseudogap: an analogy between classical and electronic fluids
• Inferring partial crystalline order in liquids from electrical resistivity