Generalizing the molecular theory of adsorbate melting in slit pores to structurally heterogeneous walls

Abstract

The molecular theory of adsorbate melting in slit pores or near planar open surfaces is generalized to the case of arbitrary pores with a random character of the spatial distribution of adsorption centers (a fully distributed model). The states of liquid and crystalline adsorbates with regard to the contributions from vibrational motions are described using a unified molecular approach based on discrete distribution functions (the lattice gas model). Equations for the chemical potential of the adsorbate in a defect crystal and a vapor-liquid system are derived with allowance for their vibrational motion within the modified quasi-dimeric model. The concentration profile of a substance at the planar interface between two solid phases or a solid-liquid interface and inside a slit pore is calculated. Molecular distributions are calculated in a quasi-chemical approximation reflecting the effects of direct correlations of interacting particles via the Lennard–Jones potential. The transition to the averaged interaction potential of an adsorbate with structurally heterogeneous walls of slit pores, the transition to an averaged description of the lattice parameter of the system, and the problem of estimating the vibrational spectrum of the adsorption system are discussed.