Molecularly ordered inorganic frameworks in layered silicate surfactant mesophases. |
| |
Authors: | S C Christiansen D Zhao M T Janicke C C Landry G D Stucky B F Chmelka |
| |
Affiliation: | Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA. |
| |
Abstract: | Self-assembled lamellar silica-surfactant mesophase composites have been prepared with crystal-like ordering in the silica frameworks using a variety of cationic surfactant species under hydrothermal conditions. These materials represent the first mesoscopically ordered composites that have been directly synthesized with structure-directing surfactants yielding highly ordered inorganic frameworks. One-dimensional solid-state 29Si NMR spectra, X-ray diffraction patterns, and infrared spectra show the progression of molecular organization in the self-assembled mesophases from structures with initially amorphous silica networks into sheets with very high degrees of molecular order. The silicate sheets appear to be two-dimensional crystals, whose structures and rates of formation depend strongly on the charge density of the cationic surfactant headgroups. Two-dimensional solid-state heteronuclear and homonuclear NMR measurements show the molecular proximities of the silica framework sites to the structure-directing surfactant molecules and establish local Si-O-Si bonding connectivities in these materials. |
| |
Keywords: | |
|
|