Negative linear compressibility in confined dilatating systems

TL;DR

This paper investigates how a fluctuating confining slit can induce negative linear compressibility in a confined fluid, revealing a coupling mechanism that causes a pseudo-critical state with unique properties.

Contribution

It introduces a theoretical and simulation-based analysis of negative linear compressibility in confined fluids, highlighting the role of matrix response and fluid-slit interactions.

Findings

Negative linear compressibility can be achieved through specific slit and fluid parameters.

Coupling effects induce a pseudo-critical state with divergent compressibility.

Switching from positive to negative compressibility involves an abrupt packing change.

Abstract

The role of a matrix response to a fluid insertion is analyzed in terms of a perturbation theory and Monte Carlo simulations applied to a hard sphere fluid in a slit of fluctuating density-dependent width. It is demonstrated that a coupling of the fluid-slit repulsion, spatial confinement and the matrix dilatation acts as an effective fluid-fluid attraction, inducing a pseudo-critical state with divergent linear compressibility and non-critical density fluctuations. An appropriate combination of the dilatation rate, fluid density and the slit size leads to the fluid states with negative linear compressibility. It is shown that the switching from positive to negative compressibility is accompanied by an abrupt change in the packing mechanism.