Self-assembly of layered aluminum silsesquioxanes: Clay-like organic-inorganic nanocomposites

A series of layered silicate-like structures with a wide range of Si/Al ratios that have an organic functionality directly bonded to the structural Si atom by Si-C bond were prepared by template sol-gel synthesis at room temperature and pressure. XRD patterns indicate that organic functionalities in the interlayers are in paraffin-like arrangement and do not interpenetrate. Structural ordering is primarily governed by the assembly of the organic functionalities into lamellar micelles. Nanocomposites were studied by solid state Si-29 and Al-27 NMR to determine the degree of condensation of inorganic framework. The results indicate that Si-O-Al linkages do not form in gels precipitated at low pH. Stable Si-O-Al linkages form when pH of the precipitates is raised. The highest degree of Si-O-Al bonding is obtained when Al solutions are prehydrolyzed prior to the addition of silane.