(242c) Monte-Carlo Simulation of the Capillary Condensation Hysteresis In Overlapping Spherical Cavities

Many porous materials possess cage-like mesopores connected into a three-dimensional network. These materials typically exhibit the capillary condensation hysteresis of type H2 with a sharp desorption branch, which originated either form the pore-blocking or cavitation mechanisms of evaporation [1]. In this work we study the specifics of pore emptying mechanism during desorption in the model of overlapping spherical cavities, which realistically represents the pore structure of mesoporous solids templated on colloidal crystals, such as 3DOm carbons [2]. We performed Monte-Carlo (MC) simulations of Lennard-Jones (LJ) nitrogen adsorption/desorption in our system. The solid surface was modeled as a number of uniformly distributed LJ sites. Grand canonical MC was used to estimate the relative pressure of desorption and adsorption in an open system, while gauge cell studies determined the pressure of equilibrium pore emptying (P_e) via Maxwell’s law of equal areas. The presence of an opening between spheres shifts P_e to the lower values comparing with the pressure corresponding to the single pore model. Pore emptying in equilibrium fashion complies with the H1 type of hysteresis which is observed experimentally for 3DOm carbons [2].

[1] Rasmussen, C. J.; Vishnyakov, A.; Thommes, M; Smarsly, B. M.; Kleitz, F.; Neimark, A.V. Langmuir. 2010; 26(12):10147-57.

[2] Fan, W.; Synder, M. A.; Sandeep, K.; Lee, S. P.; Yoo, C. W.; McCormick, A. V.; Penn, L. R.; Stein, A.; Tsapatsis, M. Nature Materials 2008; 7(12):984-91.