Reaction of organosilicon hydrides with inorganic surfaces: An example of surface catalyzed self-assembly, and, Water porosimetry: A new technique to characterize hydrophobic porous surfaces and wetting in nano-confinement

Part I. The solution phase reactions of octadecylsilane (C18H37SiH3) with 10 high surface area metal oxides (Groups II-VIII) were investigated. C18H37SiH 3 reacted with most metal oxides at room temperature and produced closely-packed supported monolayers (self-assembled monolayers, SAMs) with a high degree of order and a grafting density of C18 ∼4.5-5 groups/nm 2. According to the FTIR and 29Si NMR, molecules in the SAMs demonstrated "horizontal" cross-linking (Si-O-Si and Si-OH...HO-Si bonds) and little or no "vertical" bonds with the metal oxide (Si-O-M). Approximately 3 moles of H2 were formed per each mole of grafted C18, indicating complete hydrolysis of C18H37SiH3 during the reaction. No hydrolysis of C18H37SiH 3, however, was observed in the solution. Based on the activity of different metal oxides, we concluded that the hydrolysis of C18H37SiH 3, the key step in the reaction mechanism, is catalyzed by water adsorbed on acidic and basic centers (Lewis and Bronsted) of the surface of metal oxide.; Part II. Characterization of wetting and adhesion in a nano-confined environment is of great fundamental interest due to its application in material science. This work describes a new experimental technique that provides insight into the wetting of hydrophobic surfaces in mesopores. This method utilizes the intrusion of water into the pore space of hydrophobic porous solids. The applicability of the method has been demonstrated for a series of mesoporous silicas hydrophobized with monolayers of n-alkyldimethylchlorosilanes (1-18 carbon atoms in alkyl chain). The analysis of the water intrusion porograms allows for valuable characteristics of surfaces in pores to be obtained (which can not be evaluated using other methods) such as: volume of hydrophobic pores, water contact angles in pores, thickness of grafted monolayers, and molar volume of grafted molecules. (Abstract shortened by UMI.)...