Analysis of a Self-Consistent Description of Equilibrium Menisci and the Size Dependence of Their Formation in Slitlike
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ICOCHEMICAL PROCESSES AT THE INTERFACES
Analysis of a Self-Consistent Description of Equilibrium Menisci and the Size Dependence of Their Formation in Slitlike Pores E. S. Zaitsevaa, E. E. Gvozdevaa, and Yu. K. Tovbina, * aKurnakov
Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, Russia *e-mail: [email protected] Received October 10, 2019; revised December 27, 2019; accepted January 9, 2020
Abstract—The distribution of the density of the adsorbate inside the transition region of the liquid–vapor interface in a slit pore, in which the density of the substance varies both along the pore width and along the transition region between the vapor and the liquid, has been investigated. Equilibrium molecular distributions at the phase boundary are described in the framework of the discrete-continuum molecular theory in the quasi-chemical approximation, which reflects the effects of direct correlations of interacting particles. The interaction of particles is described by a pair potential of the Lennard–Jones type. The self-consistency of the description of the rough meniscus profile using kinetic (through the equality of the calculated desorption and condensation rates) and equilibrium equations has been established. The probability of the formation of a liquid phase bridge between the pore walls in slotlike porous systems is considered depending on the length of the section, the pore width and the energy of the walls. Keywords: molecular theory, adsorption, porous systems, stratification in pores, meniscus vapor–liquid, adsorption rates, desorption rates, bridges DOI: 10.1134/S207020512006026X
INTRODUCTION The nature of the distribution of the adsorbed substance in porous materials plays an important role in the processes of equilibrium adsorption and the processes of transfer of substances through them [1–12]. These processes are multifactorial: the adsorption characteristics are influenced not only by the temperature and the type of the adsorbate–adsorbent system, but also by the structural parameters of the porous material, reflecting the pore width, their length, and the presence of distortions in pore geometry from traditional ideal structures. Recently, in the study of the properties of the adsorbate–adsorbent system, modeling methods based on information on interparticle potential functions have played an active role [12–15]. This paper discusses two issues of microscopic modeling of adsorption in slit pores with the formation of a meniscus by the “vapor in a pore”–“liquid in a pore” transition region, which have not been previously studied. The first question concerns the selfconsistency of the description of the pore meniscus from the standpoint of the equilibrium theory and from the point of view of dynamic transport processes by different mechanisms. The idea of a self-consistent description of the rates of kinetic processes and equilibrium in imperfect and inhomogeneous systems is key for the relationship between equilibrium and
kinetics, as the passage to the limit in time.
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