Time-resolved fluorescence quenching studies in nanocomposite materials made of silica and cetyltrimethylammonium bromide

Fluorescence quenching studies have been performed in silica/cetyltrimethylammonium bromide nanocomposite materials made by the sol-gel method and by mixing prehydrolyzed tetramethoxysilane with aqueous surfactant micelles. Hydrophobic probes incorporated in these materials are solubilized in the:surfactant subphase where they can diffuse. Pyrene forms diffusion-controlled excimers there. The subphase is organized, providing a polar hydrocarbon interface and a hydrophobic interior, and it most probably consists of percolating surfactant clusters, each formed by fusion of several micelles. Hydrophilic molecules are incorporated in the embedding silica phase, and they are immobilized. Quenching is much more restricted in films than in bulk matrices, even though films support a large number of molecular layers. This result is consistent with the existence of alternating surfactant bilayer/silica layer structure, previously proposed.