(620c) NMR Cryoporometry As a Complementary Characterization Technique

Gas sorption measurements are routinely used for characterizations of mesoporous solids. With better understanding of fluid behavior in confined spaced of materials with complex pore structures and with the development of novel DFT approaches, this method nowadays provides a considerable accuracy in structural analysis. In recent two decades, NMR cryoporometry has emerged as a novel experimental technique, which can provide better spatial resolution as compared to conventional nitrogen sorption measurements. Quantitative analysis of the data obtained using NMR cryoporometry, however, still remain quite approximate due to an incomplete understanding of underlying physical processes and the lack of microscopic approaches similar to those used for modeling gas-liquid equilibria. By means of experiments and theoretical modeling, we have obtained deeper insights into mechanisms controlling solid-liquid transitions in disordered mesoporous solids. Thus, using NMR cryoporometry as an experimental technique and Vycor porous glass as a model system, we have performed first detailed experimental studies of melting and freezing scanning behavior, namely melting/freezing patterns following incomplete freezing/melting of the confined fluid. This type of experiments has yielded additional information on thermodynamics of the transition processes. The experimental results have been analyzed with the help of a microscopic model of crystal growth adopted for confined fluids. In this way, we have qualitatively reproduced most of experimental findings reported so far in the literature.