Temperature Dependence of the Longitudinal Modulus of Liquid Argon in Nanopores

Schappert, Klaus; Pelster, R.

doi:10.1021/acs.jpcc.7b12839

Cited by 13 publications

(53 citation statements)

References 57 publications

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“…The longitudinal modulus of the sample, however, behaves differently: while not changing appreciably at low vapor pressures, it rises abruptly at the capillary condensation point. This behavior is consistent with the ultrasonic measurements performed for other adsorbates: n -hexane , and argon. − …”

Section: Introductionsupporting

confidence: 89%

Molecular Simulations Shed Light on Potential Uses of Ultrasound in Nitrogen Adsorption Experiments

Maximov

Gor

2018

Langmuir

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Nitrogen adsorption is one of the main characterization techniques for nanoporous materials. The experimental adsorption isotherm provides information about the surface area and pore size distribution (PSD) for a sample. In this work we show that additional insight into PSD can be gained when the speed of sound propagation through a sample is measured during nitrogen adsorption experiment. We analyzed published experimental data on ultrasound propagation through a nanoporous Vycor glass sample during nitrogen adsorption experiment. Next, we calculated the change of the longitudinal and shear moduli of the sample as a function of relative vapor pressure. From this, we show that the shear modulus of the sample does not change upon filling the pores, evidencing that adsorbed nitrogen at 77 K has zero shear modulus, similarly to a bulk liquid. The longitudinal modulus of the sample behaves differently: it changes abruptly at the capillary condensation and keeps gradually increasing thereafter. We performed Monte Carlo molecular simulations to predict the compressibility of adsorbed nitrogen and then calculated the longitudinal modulus of the nitrogen-saturated Vycor using the Gassmann equation. Our theoretical predictions nicely matched the longitudinal modulus derived from the experimental data. Additionally, we performed molecular simulations to model nitrogen adsorbed in silica pores of sizes ranging from 2 to 8 nm. We found that the isothermal elastic modulus of adsorbed nitrogen depends linearly on the inverse pore size. This dependence, along with the proposed recipe for probing the modulus of adsorbed nitrogen, sets up the grounds for extracting additional information about the porous samples, when the nitrogen adsorption is combined with ultrasonic experiments.

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Section: Introductionsupporting

confidence: 89%

Molecular Simulations Shed Light on Potential Uses of Ultrasound in Nitrogen Adsorption Experiments

Maximov

Gor

2018

Langmuir

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“…This method for the determination of f requires that the adsorbate is liquid and possesses a vanishing shear modulus (and in this case, it yields the same results as volumetric measurements). 36,38 From previous measurements, we know that solid argon is only present for temperatures below T ≈ 75.8 K. 11 Furthermore, the variation of the relative pressure p/p 0 during a sorption isotherm causes no significant change of the effective shear modulus, i.e., in the temperature range of the measurements, the adsorbed argon behaves basically like an ideal liquid (see Figure 1 in ref 39). Simultaneously to the velocity of shear waves, c t , we have measured the velocity of longitudinal ultrasonic waves, c l , which allows the calculation of the effective longitudinal modulus β = ρ 0 (c l c t,0 /c t ) 2 , where ρ 0 denotes the density of the unfilled sample and c t,0 denotes the velocity of the shear waves propagating through the unfilled sample (see ref 36).…”

Section: Methodsmentioning

confidence: 93%

Liquid Argon in Nanopores: The Impact of Confinement on the Pressure Dependence of the Adiabatic Longitudinal Modulus

Schappert

Pelster

2018

J. Phys. Chem. C

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The elastic properties of nanoconfined argon show deviations from the behavior of bulk argon. In this paper, we study the pressure dependence of the adiabatic longitudinal modulus β Ar,ads of the adsorbate in nanoporous Vycor glass. Adsorption induces a normal pressure Δp S acting on the pore surface. As it is well known, this pressure leads to a deformation of the porous sample, but it also influences the elastic properties of the adsorbate. Ultrasonic measurements reveal a linear relation between β Ar,ads and the Laplace pressure, p L , which is a major contribution to Δp S . For the whole temperature range of the confined liquid argon (76− 86.9 K), the proportionality constant, α Ar,ads = dβ Ar,ads /dp L , is higher than that for bulk argon, i.e., the adsorbed argon exhibits a stronger dependence on pressure than bulk argon. In addition, we observe no temperature dependence of α Ar,ads , which contrasts with the clear increase of α Ar,bulk with increasing temperature. Further measurements and simulations can show how the interaction strength between adsorbate and pore surface contributes to the observed effects.

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“…Their method relies on the assumption that the modulus of the porous sample K 0 has a linear dependence on porosity at the low porosity range φ < ∼ 0.25. In a later work, [115] Schappert and Pelster showed that Eq. 27 using the value of K s for quartz gives results close to using Eq.…”

Section: Probing the Elastic Properties Of Confined Fluidsmentioning

confidence: 97%

Elastic properties of confined fluids from molecular modeling to ultrasonic experiments on porous solids

Dobrzanski

Gurevich

Gor

2021

Applied Physics Reviews

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Fluids confined in nanopores are ubiquitous in nature and technology. In recent years, the interest in confined fluids has grown, driven by research on unconventional hydrocarbon resources -shale gas and shale oil, much of which are confined in nanopores. When fluids are confined in nanopores, many of their properties differ from those of the same fluid in the bulk. These properties include density, freezing point, transport coefficients, thermal expansion coefficient, and elastic properties. The elastic moduli of a fluid confined in the pores contribute to the overall elasticity of the fluid-saturated porous medium and determine the speed at which elastic waves traverse through the medium. Wave propagation in fluid-saturated porous media is pivotal for geophysics, as elastic waves are used for characterization of formations and rock samples. In this paper, we present a comprehensive review of experimental works on wave propagation in fluid-saturated nanoporous media, as well as theoretical works focused on calculation of compressibility of fluids in confinement. We discuss models that bridge the gap between experiments and theory, revealing a number of open questions that are both fundamental and applied in nature. While some results were demonstrated both experimentally and theoretically (e.g. the pressure dependence of compressibility of fluids), others were theoretically predicted, but not verified in experiments (e.g. linear scaling of modulus with the pore size). Therefore, there is a demand for the combined experimental-modeling studies on porous samples with various characteristic pore sizes. The extension of molecular simulation studies from simple model fluids to the more complex molecular fluids is another open area of practical interest.

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Temperature Dependence of the Longitudinal Modulus of Liquid Argon in Nanopores

Cited by 13 publications

References 57 publications

Molecular Simulations Shed Light on Potential Uses of Ultrasound in Nitrogen Adsorption Experiments

Molecular Simulations Shed Light on Potential Uses of Ultrasound in Nitrogen Adsorption Experiments

Liquid Argon in Nanopores: The Impact of Confinement on the Pressure Dependence of the Adiabatic Longitudinal Modulus

Elastic properties of confined fluids from molecular modeling to ultrasonic experiments on porous solids

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