Hybrid Organic−Inorganic Quaternary Ammonium Organosilane Functionalized Mesoporous Thin Films

Quaternary ammonium functionalized mesoporous thin films were prepared by spin casting mixtures of bis-(triethoxysilyl)ethane hexaethoxydisilethylene with a series of quaternary ammonium functionalized organosilanes that primarily differed only in the length of the hydrocarbon segment: N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride; N,N-didecyl-N-methyl-(3-trimethoxysilyl-propyl)ammonium chloride; tetradecyldimethyl-(3-trimethoxysilyl-propyl)ammonium chloride; and octadecyldimethyl-(3-trimethoxysilyl-propyl)ammonium chloride. X-ray diffraction revealed that the films formed with the longest hydrocarbon segment (18 carbons) did not exhibit an ordered structure, while the remainder of the films exhibited p6mm pore ordering. These films remained ordered following surfactant extraction and calcination, with some film shrinkage occurring following either procedure. The d-spacing of the films was found to decrease linearly with increasing length of the ammonium chloride hydrocarbon segment. As determined by XPS studies, the longer hydrocarbon chain length organosilanes (n ≥ 10) were also found to incorporate more efficiently into the films than the shorter chain material.