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In gas adsorption studies, porous glasses are frequently referred to as model materials for highly disordered mesopore systems. Numerous works suggest that an accurate interpretation of physisorption isotherms requires a complete understanding of network effects upon adsorption and desorption, respectively. The present article deals with nitrogen and argon adsorption at different temperatures (77 and 87 K) performed on a series of novel nanoporous glasses (NPG) with different mean pore widths. NPG samples contain smaller mesopores and significantly higher microporosity than porous Vycor glass or controlled pore glass. Since the mean pore width of NPG can be tuned sensitively, the evolution of adsorption characteristics with respect to a broadening pore network can be investigated starting from the narrowest nanopore width. With an increasing mean pore width, a H2-type hysteresis develops gradually which finally transforms into a H1-type. In this connection, a transition from a cavitation-induced desorption toward desorption controlled by pore blocking can be observed. Furthermore, we find concrete hints for a pore size dependence of the relative pressure of cavitation in highly disordered pore systems. By comparing nitrogen and argon adsorption, a comprehensive insight into adsorption mechanisms in novel disordered materials is provided.

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Freezing and melting behavior of nitrobenzene confined to pores of Vycor porous glass with random pore structure has been studied by means of nuclear magnetic resonance cryoporometry. The two transitions are found to reveal a broad hysteresis. To get deeper insight into the mechanisms leading to this phenomenon, scanning experiments exploiting temperature reversal upon incomplete freezing or melting have been performed. In this way, it was found that different cooling and warming histories result in different solid-liquid configurations within the pore system. Further evolution of the thus-attained configurations with changing temperature unveiled important information about the transition paths. In particular, these experiments indicated the occurrence of a pronounced pore blocking for freezing, resulting in freezing transitions via invasion percolation. The melting, on the other hand, is found to occur homogeneously over the whole pore network.