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

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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.