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

聚乙二醇（PEG）和相关的cmen型非离子表面活性剂具有多种良好的性能（蒸气压低、无毒、可生物降解等），使其成为化学反应的绿色溶剂。此外，它们可以应用于支持的液相系统中，其中它们嵌入在介孔二氧化硅基体中。为了充分利用它们作为溶剂的潜力，有必要了解它们的物理化学性质，它们与支撑表面的相互作用，以及它们在孔隙限制下的相行为。纯聚乙二醇的初步分子动力学（MD）研究、实验固态核磁共振（ssNMR）和约束下聚乙二醇的热力学研究表明，聚乙二醇和cmen型表面活性剂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的重要性。为了进一步了解这些分子内和分子间相互作用的细节，将对具有源自1-辛醇（C8E0）结构的模型分子进行ssNMR，热力学和MD模拟研究。利用这些模型，首先考察了在1-辛醇基结构中放置醚官能团对分子内和分子间氢键行为的影响。其次，研究了链烷基和支链烷基非离子表面活性剂在约束条件下的行为差异。我们将用一组系统的功能化多孔材料来模拟这种约束，以阐明通过香兰素和氨丙基三乙基氧基硅烷（APTES）表面修饰固定在介孔二氧化硅上的Pd催化剂中，受约束分子与表面功能化的相互作用。这些研究的综合结果将为以PEG和cmen型非离子表面活性剂为反应介质的非均相过渡金属催化反应环境提供详细的分子水平见解。

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.