Transition in fluctuation behaviour of normal liquids under high pressures

TL;DR

This study investigates how fluctuation behavior in normal liquids changes under high pressures, revealing a transition from exponential decay to longer correlations linked to molecular packing and density fluctuations.

Contribution

It identifies a pressure-induced transition in fluctuation behavior and links it to molecular packing changes, expanding understanding of liquid properties under extreme conditions.

Findings

Existence of two fluctuation regimes in liquids under high pressure

Identification of a crossing point of isobaric expansion coefficient isotherms

Correlation between fluctuation behavior and molecular packing changes

Abstract

We explore the behaviour of the inverse reduced density fluctuations and the isobaric expansion coefficient using {\alpha},{\omega}-dibromoalkanes as an example. Two different states are revealed far from the critical point: the region of exponentially decaying fluctuations near the coexistence curve and the state with longer correlations under sufficiently high pressures. The crossing of the isotherms of the isobaric expansion coefficient occurs within the PVT range of the mentioned transition. We discuss the interplay of this crossing with the changes in molecular packing structure connected with the analysed function of the density, which represents inverse reduced volume fluctuations.