Connect the Thermodynamics of Bulk and Confined Fluids: Confinement-Adsorption Scaling

Abstract

A fluid (a gas or a liquid) adsorbed in a porous material can behave very differently from its bulk counterpart. The advent of various synthesized materials with nanopores and their wide applications have provided strong impetus for studying fluids in confinement because our current understanding is still incomplete. From a large number of Monte Carlo simulations, we found a scaling relation that allows for connecting some thermodynamic properties (chemical potential, free energy per particle, and grand potential per particle) of a confined fluid to the bulk ones. Upon rescaling the adsorbed fluid density, the adsorption isotherms for many different confining environments collapse to the corresponding bulk curve. We also reveal the intimate connection of the reported scaling relation to Gibbs theory of inhomogeneous fluids and morphological thermodynamics. The advance in our understanding of confined fluids, gained from this study, also opens attractive perspectives for circumventing experimental difficulty for directly measuring some fluid thermodynamic properties in nanoporous materials.

Enhancing Gas Solubility in Nanopores: A Combined Study Using Classical Density Functional Theory and Machine Learning

“…The interaction for unlike pairs is calculated using the Lorentz–Berthelot (LB) combination rules, i.e., and σ ij = (σ ii + σ jj )/2. As shown in our previous work, the porosity (pore size) and the fluid–solid interaction are of primary importance for determining the thermodynamics of confined fluids; the other characteristics, such as pore connectivity, pore size distribution, etc., play a less significant role. Hence, in this work, the porous material has been simplified as a simple slit pore model.…”

Structural and Dynamical Behaviour of Colloids with Competing Interactions Confined in Slit Pores

“…In particular, the cluster-crystal is able to survive up to T * = 0.30 when confined in pores of sizes W * = 5, 7 and 11, whereas in bulk it melts at T * = 0.20 − 0.25 depending on the density. Shifts in the coexistence lines between two phases are common under confinement and have been observed either in complex [26,27,35] and simple [36] fluids. On the contrary, for the pore size W * = 9, the structure remains only partially ordered down to T * = 0.20.…”

Confinement of Colloids with Competing Interactions in Ordered Porous Materials

“…The fact that the FCC crystal is able to survive up to higher chemical potentials than in bulk is evidence of the high stability of this crystal but also of the phase diagram shift experienced by fluids under confinement. 15,16 Confinement in the D Material. Next, we focus on the diamond porous structure.…”

“…In this situation, the confined fluid prefers to organize again into nearly spherical clusters, arranged in the FCC lattice similar to the behavior observed at a lower chemical potential. The fact that the FCC crystal is able to survive up to higher chemical potentials than in bulk is evidence of the high stability of this crystal but also of the phase diagram shift experienced by fluids under confinement. , …”

“…Confinement offers an extra parameter to control the behavior of complex colloidal systems. It has been demonstrated in experiments − and simulations − that systems with competing interactions under confinement exhibit new thermodynamic as well as structural properties. When confined, several novel structures that are not observed in bulk may be created by tuning the shape of the confining walls. ,,− , An interesting approach to exploit all the possibilities that confinement offers is template-assisted fabrication.…”