Abstract
This work studies how morphology (i.e., the shape of a structure) and topology (i.e., how different structures are connected) influence wall adsorption and capillary condensation under tight confinement. Numerical simulations based on classical density functional theory (cDFT) are run for a wide variety of geometries using both hard-sphere and Lennard-Jones fluids. These cDFT computations are compared to results obtained using the Minkowski functionals. It is found that the Minkowski functionals can provide a good description of the behavior of Lennard-Jones fluids down to small system sizes. In addition, through decomposition of the free energy, the Minkowski functionals provide a good framework to better understand what are the dominant contributions to the phase behavior of a system. Lastly, while studying the phase envelope shift as a function of the Minkowski functionals it is found that topology has a different effect depending on whether the phase transition under consideration is a continuous or a discrete (first-order) transition.
Highlights
Under tight confinement, a gas can form a condensed phase at a pressure below the bulk vapor pressure
We study the effect of topology on capillary condensation and wall adsorption under confinement through the lens of the Minkowski functionals
The effect of morphology and topology on capillary condensation is studied in a systematic manner using a Minkowski functional framework
Summary
A gas can form a condensed phase at a pressure below the bulk vapor pressure. It states that in many cases, the free energy of a system, or any other functional, can be expressed as a linear combination of Minkowski functionals [30,31], decoupling the thermodynamical behavior of a system from its morphology and topology This has two important consequences: (i) Characterization and classification; when the assumptions of Hadwiger’s theorem are fulfilled, the Minkowski functionals provide a complete spatial description of a physical system. Classical density functional theory (cDFT) is employed [33] to compute the free energy and adsorption of a Lennard-Jones fluid for a wide variety of geometries This simulation technique is commonly used to study capillary condensation and wetting [34,35,36,37] and can capture larger length scales than molecular dynamics simulations. The reason behind this intriguing behavior is still under active investigation
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