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

[807180 . tolbert]本项目通过实验直接探索控制有序二氧化硅/表面活性剂介结构复合材料稳定性的热力学和动力学因素。这些令人兴奋的新材料由有组织的有机成分组成，它控制着长期的周期性，而无机框架则提供了稳定性和强度。重要的是，有机成分可以去除，以生产有序的介孔材料，具有广泛的应用潜力。动力学现象似乎在这些材料的形成中起着重要作用，因此了解这些动力学效应将对未来材料的合理设计非常有用。这些材料的相变将实时跟踪，以深入了解控制结构的驱动力和动力学因素。设想了两类实验：第一组涉及热液条件下的结构变化，以响应热和化学处理。通过系统地改变有机组分和二氧化硅骨架聚合的程度，转变动力学揭示了有机填料和刚性无机二氧化硅骨架之间的相互作用。实时x射线散射和固态核磁共振波谱将用于跟踪结构变化，并了解长期周期性和局部键合的演变。第二组实验通过考察相在高压下的行为，直接探讨了填料约束的作用。在这里，这些复合材料在非水热条件下重组的能力将被确定。这些实验为分离表面活性剂填料和二氧化硅聚合的作用提供了希望。研究周期性二氧化硅/表面活性剂纳米结构材料的相稳定性动力学将提供可直接用于合成新型二氧化硅/表面活性剂复合材料的信息，其目标是学习如何在动力学上捕获或热力学上有利于新的复合材料或介孔结构，以用于催化、分离或化学传感等特定应用

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.***