The Kinetics of Phase Stability in Periodic Silica/Surfactant Nanostructured Materials

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9807180TolbertThis project involves experiments which directly probe the thermodynamic and kinetic factors controlling stability in ordered silica/surfactant mesostructured composites. These exciting new materials consist of an organized organic component, which controls long range periodicity, and an inorganic framework, which provides stability and strength. Importantly, the organic component can be removed to produce ordered mesoporous materials which have potential for a wide range of applications. Kinetic phenomena appear to play a major role in the formation of these materials and thus understanding these kinetic effects would be enormously useful for the rational design of future materials. Phase transitions in these materials will be followed in real time to gain insight into the driving forces and kinetic factors controlling structure. Two classes of experiments are envisioned: The first set involves structural changes under hydrothermal conditions in response to thermal and chemical treatments. By systematically varying the organic moieties and the degree of silica framework polymerization, transition kinetics reveal the interplay between organic packing and the rigid inorganic silica framework. Real-time X-ray scattering and solid-state NMR spectroscopy will be utilized to follow structural change and to learn about the evolution of both long range periodicity and local bonding. The second set of experiments directly probe the role of packing constraints by examining phase behavior under high pressure. Here, the ability of these composites to reorganize under non-hydrothermal conditions will be determined. These experiments offer hope for separating the role of surfactant packing from that of silica polymerization.%%%Addressing the kinetics of phase stability in periodic silica/surfactant nanostructured materials will provide information that can be directly used to synthesize new classes of silica/surfactant composites, with the goal of learning how to kinetically trap or thermodynamically favor new composite or mesoporous structures for specific applications in catalysis, separations, or chemical sensing.***