Exchange Dynamics at the Interface of Nanoporous Materials with their Surroundings

The evolution of transient concentration profiles in nanoporous materials is shown to provide direct information about the rate of molecular exchange at the interface of these materials with the surrounding atmosphere. This includes the quantitation of a surface permeability and, related with each other, of the sticking factor, i.e., of the probability that a molecule colliding with the external surface from the outside atmosphere, will in fact enter the genuine pore system of the material under study. Owing to the recent introduction of interference microscopy to this type of systems, the relevant experimental evidence has become directly accessible and is applied to two model systems which are found to differ notably in their interface dynamics.