Thermodynamic behavior of supercritical matter

TL;DR

This paper investigates the thermodynamic properties of supercritical fluids, revealing a crossover in specific heat and developing a theory that explains these behaviors without relying on system-specific details.

Contribution

It introduces a novel thermodynamic theory for supercritical matter that accounts for a specific heat crossover and matches experimental data without free parameters.

Findings

Discovery of a specific heat crossover in supercritical fluids

Development of a theory matching experimental specific heat data

Derivation of supercritical scaling exponents and power law

Abstract

Since their discovery in 1822, supercritical fluids have been of enduring interest, and have started to be deployed in many important applications. Theoretical understanding of the supercritical state is lacking, and is seen to limit further industrial deployment. Here, we study thermodynamic properties of the supercritical state, and discover that specific heat shows a crossover between two different regimes, an unexpected result in view of currently perceived homogeneity of supercritical state in terms of physical properties. We subsequently formulate a theory of system thermodynamics above the crossover, and find good agreement between calculated and experimental specific heat with no free fitting parameters. We derive a power law and analyze supercritical scaling exponents in the system above the Frenkel line. In this theory, energy and heat capacity are governed by the minimal length of the longitudinal mode in the system only, and do not explicitly depend on system-specific structure and interactions.