Characterization of the Properties and Phase Behavior of nonionic Surfactants confined in mesoporous Silica Materials employing Solid State NMR Techniques

聚乙二醇及其相关的CmEn型非离子表面活性剂具有低蒸汽压、无毒、可生物降解性等优良性能。这使得它们能够被用作化学反应的绿色溶剂。此外，它们还可以应用于负载在介孔二氧化硅基质中的支持液相体系。为了充分开发它们作为溶剂的潜力，有必要了解它们的物理化学性质，它们与载体表面的相互作用，以及它们在限制孔中的相行为。聚乙二醇单分子动力学(MD)的初步研究以及聚乙二醇在受限条件下的实验固体核磁共振和热力学研究表明，聚乙二醇型和CmEn型表面活性剂的分子内和分子间氢键相互作用对于理解它们与孔表面的相互作用具有重要意义。为了进一步了解分子内和分子间相互作用的细节，将对具有1-辛醇(C8E0)结构的模型分子进行ss核磁共振、热力学和分子动力学模拟研究。利用这些模型，首先考察了乙醚官能团在正辛醇碱结构中的放置对分子内和分子间氢键行为的影响。其次，研究了直链和支链非离子表面活性剂在受限条件下的行为差异。这种限制将通过一组系统的功能化多孔材料来模拟，以阐明通过香兰素和氨基丙基三乙氧基硅烷(APTES)表面修饰固定在介孔二氧化硅上的Pd催化剂中受限分子与表面官能化的相互作用。这些研究的综合结果将提供关于以聚乙二醇型和CmEn型非离子表面活性剂为反应介质的多相过渡金属催化反应环境的详细的分子水平的见解。

Polyethylene glycol (PEG) and related CmEn-type nonionic surfactants contain a variety of favorable properties (low vapor pressure, non-toxicity, biodegradability etc.) that enable them to be used as green solvents for chemical reactions. In addition, they can be applied in supported liquid phase systems, where they are embedded in a mesoporous silica matrix. To fully exploit their potential as solvents, it is necessary to understand their physicochemical properties, their interactions with the support surface, and their phase behavior in the confinement of the pores. Preliminary molecular dynamics (MD) studies of neat PEG as well as experimental solid-state NMR (ssNMR) and thermodynamic studies of PEG under confinement have illustrated the importance of intra- and intermolecular hydrogen bonding interactions in PEG and CmEn-type surfactants for understanding their interactions with pore surfaces. To further discern the details of these intra- and intermolecular interactions, ssNMR, thermodynamic and MD simulation studies will be carried out on model molecules that possess structures derived from 1-octanol (C8E0). With these models, firstly the effect of the placement of an ether functional group in the 1-octanol base structure on the intra- and intermolecular hydrogen bonding behavior will be inspected. Secondly, differences between nonionic surfactants with linear and branched alkyl chains in their behavior under confinement will be studied. The confinement will be mimicked by a systematic set of functionalized porous materials, to elucidate the interactions of the confined molecules with the surface functionalization present in Pd catalysts immobilized onto mesoporous silica through vanillin and aminopropyltriethoxysilane (APTES) surface decorations. The combined results from these studies will provide detailed molecular level insights about the reaction environment in heterogeneous transition metal catalysis using PEG and CmEn-type nonionic surfactants as the reaction medium.