Fluid-fluid interfaces in metal-organic frameworks

Grandcanonical Monte Carlo simulations in combination with successive umbrella sampling are used to study interfaces in the metal- organic frameworks ( MOFs) IRMOF- 1 and IRMOF- 8. These interfaces are between coexisting phases of methane ( CH4) fluids that form on the surface of the framework structures of the latter MOF systems. Approaching the critical point of the corresponding demixing transition, the interfacial free energy as well as the interfacial width show a power- law scaling, as expected for the universality class of the three- dimensional Ising model. Capillary waves are strongly suppressed due to the external potential imposed by the framework structure. In IRMOF- 8, density profiles of inhomogeneous systems with fluid- fluid interfaces show pronounced oscillations due to the crystalline framework structure. [GRAPHICS]