Modulus-Pressure Equation for Confined Fluids

TL;DR

This study investigates how the elastic modulus of fluids changes with pressure in confined nanoporous environments, revealing that the slope of this relationship remains consistent despite confinement effects, enabling estimation of porous medium properties.

Contribution

The paper introduces a method to determine the elastic modulus of confined fluids using the slope of the modulus-pressure relation, validated through Monte Carlo simulations and experimental data.

Findings

The slope of the modulus-pressure relation is unaffected by confinement and temperature.

Simulated and experimental data show good agreement for the slope of the modulus-pressure relation.

The slope can be used to estimate elastic moduli of unknown porous media.

Abstract

Ultrasonic experiments allow one to measure the elastic modulus of bulk solid or fluid samples. Recently such experiments have been carried out on fluid-saturated nanoporous glass to probe the modulus of a confined fluid. In our previous work [J. Chem. Phys., (2015) 143, 194506], using Monte Carlo simulations we showed that the elastic modulus $K$ of a fluid confined in a mesopore is a function of the pore size. Here we focus on modulus-pressure dependence $K(P)$, which is linear for bulk materials, a relation known as the Tait-Murnaghan equation. Using transition-matrix Monte Carlo simulations we calculated the elastic modulus of bulk argon as a function of pressure and argon confined in silica mesopores as a function of Laplace pressure. Our calculations show that while the elastic modulus is strongly affected by confinement and temperature, the slope of the modulus versus pressure is not. Moreover, the calculated slope is in a good agreement with the reference data for bulk argon and experimental data for confined argon derived from ultrasonic experiments. We propose to use the value of the slope of $K(P)$ to estimate the elastic moduli of an unknown porous medium.