Pseudocritical or hysteresis temperature versus pore size for simple fluids confined in cylindrical nanopores.
The adsorption/desorption isotherms measured in nanoporous materials generally present a hysteresis. The hysteresis shrinks upon increasing the temperature (for a given pore size) or decreasing the pore size (for a given temperature), until it finally disappears at the so-called hysteresis (or pseudocritical) temperature T(h) or hysteresis (or pseudocritical) pore size R(h), not to be confused with a true critical point. In this paper, a Monte Carlo approach allowed calculating the surface free energy of confined fluid along the adsorption/desorption isotherms for various cylindrical pore sizes and temperatures. A simple phenomenological model then allowed exploiting these results to determine the relation between T(h) and R(h). The prediction is compared to various literature models and experimental data, showing agreement within uncertainties. On the other hand, the simulations cannot be used directly to predict T(h) and R(h) since they significantly overestimate the hysteresis width. The model predicts a nonlinear relation between the reduced hysteresis temperature and the inverse pore radius.
Puibasset
Joël
J
Centre de Recherche sur la Matière Divisée, CNRS-Université d'Orléans, 1b rue de la Férollerie, 45071 Orléans Cedex 02, France. puibasset@cnrs-orleans.fr