Molecular simulation of adsorption and intrusion in nanopores

Abstract

International audienceThis paper reports Monte Carlo simulations of the adsorption (wetting fluid) or intrusion (non-wetting fluid) in cylindrical silica nanopores. All the pores are opened at both ends towards an external bulk reservoir, so that they mimic real materials for which the confined fluid is always in contact with the external phase. This realistic model allows us to discuss the nature of the filling and emptying mechanisms that are observed in the experiments. The adsorption corresponds to the metastable nucleation of the liquid phase, starting from a partially filled pore (a molecular thick film adsorbed at the pore surface). On the other hand, the desorption occurs through the displacement at equilibrium of a gas/liquid hemispherical interface (concave meniscus) along the pore axis. The intrusion of the non-wetting fluid proceeds through the invasion in the pore of the liquid/gas interface (convex meniscus), while the extrusion consists of the nucleation of the gas phase within the pore. In the case of adsorption, our simulation data are used to discuss the validity of the modified Kelvin equation (which is corrected both for the film adsorbed at the pore surface and for the curvature effect on the gas/liquid surface tension)

Synthesis and Textural Characterization of Mesoporous and Meso-/Macroporous Silica Monoliths Obtained by Spinodal Decomposition

“…For spherical pores, the constriction diameter of the pore is calculated from the pressure of the closing point of the hysteresis by applying the BdB desorption and the cavity size is calculated from the adsorption branch of the isotherm by applying the BdB desorption to the mean pressure of adsorption ( Figure 7). This observation has been confirmed by simulation experiments on various shapes of pores [28][29][30]. pores.…”

A critical assessment of capillary condensation and evaporation equations: A computer simulation study

“…On desorption, the evaporation occurs at a relative pressure of 0.18, which is marginally lower than the condensation pressure, and is typically observed for argon in small cylindrical pores of finite length at low temperature [40]. It is noted that a study of a desorption meniscus is not possible for simulations in an infinite pore [24,40].…”

“…One point to note in Fig. 5 is that the isosteric heat is always greater than the heat of condensation, which is different from adsorption on a flat surface where the heat approaches the condensation heat at high loadings [24]. This is due to the enhancement effects of the curvature of the cylindrical pore.…”

“…Numerous contributions to the study of condensation and evaporation in single pores have used computer simulation [24][25][26][27][28][29] as well as studies of more complex geometries [30][31][32][33][34].…”

Computer analysis of the microporous structure of activated carbon fibres using the fast multivariant identification procedure of adsorption system parameters

“…Several different equations have been proposed to describe the adsorption equilibrium, among which the most popular are: the Dubinin-Radushkevich equation [80], the Dubinin-Astakhov equation [81,82], and the BET equation [83]. The development of computer science and the improvements in computational technology have triggered the development of more advanced methods of pore structure description, based on sophisticated numerical tools [84], statistical mechanics, computer simulations [85][86][87][88][89], the DFT technique [90][91][92], fractal geometry [93,94], and neural networks [95].…”