Phase behaviour of a simple fluid confined in a periodic porous material

Abstract

Using density functional theory for a simple fluid of hard spheres with a square-well attraction, we study the phase behaviour of the fluid confined in triply periodic porous material, where the pore space is bounded by a bicontinuous minimal surface. We combine our numerical results with the morphometric thermodynamics, an ansatz that expresses thermodynamic quantities as a linear combination of four additive geometrical terms, and analyse the dependency of the transition point between a liquid and a gas on the geometrical properties of the confining space. By demonstrating that the morphometric approach can be employed in order to account for the thermodynamic behaviour of a simple fluid in a complex porous material, we make the first step towards a better understanding of experimental observations that can help to characterise the pore space.

GRAPHICAL ABSTRACT

Keywords:

• Density functional theory
• phase behaviour
• porous material

Acknowledgments

We dedicate this paper to the memory of Gerhard Findenegg, whose careful studies of fluids in porous material inspired us to look closer at the question on how geometry and topology influences the adsorption behaviour of a fluid in a complex pore.

Disclosure statement

No potential conflict of interest was reported by the authors.