Molecular-scale remnants of the liquid-gas transition in supercritical polar fluids

TL;DR

This study reveals that supercritical polar fluids, like water, retain molecular-scale signatures of the liquid-gas transition, evidenced by a dipole density crossover linked to hydrogen bonding and the Widom line, extending our understanding of supercritical states.

Contribution

The paper introduces an electronically coarse-grained model showing persistent liquid-gas transition remnants in supercritical fluids, highlighting the role of hydrogen bonds and dipole behavior.

Findings

Crossover in dipole density correlates with hydrogen bond onset.

Crossover points align with Widom line and heat capacity maxima.

Effect observed even in dipole-limit models, indicating generality.

Abstract

An electronically coarse-grained model for water reveals a persistent vestige of the liquid-gas transition deep into the supercritical region. A crossover in the density dependence of the molecular dipole arises from the onset of non-percolating hydrogen bonds. The crossover points coincide with the Widom line in the scaling region but extend further, tracking the heat capacity maxima, offering evidence for liquid- and gas-like state points in a "one-phase" fluid. The effect is present even in dipole-limit models suggesting that it is common for all molecular liquids exhibiting dipole enhancement in the liquid phase.