Integral Equation Theory of Adsorption in Templated Materials: Influence of Molecular Attraction

Abstract

Understanding the fundamental properties of fluids under confinement in templated porous media is important for the rational design of materials with tailored functions. However, theoretical descriptions remain elusive. Although a number of approaches have been developed within the replica Ornstein−Zernike (ROZ) formalism, they have thus far been limited mainly to simple species. Another challenge is associated with the general applicability of integral equation theories, originally developed for bulk liquids, to confined systems in general and, in particular, to molecular systems confined in templated structures. In this work, we extend our previous theory of molecular species adsorbed in a templated porous material (a ROZ solution to a reference interaction site model) to systems with attractive interactions. We explore the scope and applicability of direct routes toward the chemical potential in combination with several well-established closures, such as Percus−Yevick, mean spherical approximation, hypernetted chain closure (HNC), partially linearized HNC (PLHNC), and Martynov−Sarkisov. The relative accuracy, thermodynamic consistency, and ease of convergence are explored. Although only semiquantitative agreement can be expected from these approximate closure relations, we demonstrate that the proposed theory predicts templated molecular recognition with reasonable accuracy.