Solubilization of Aromatic Molecules in Templating Micelles of Mesoporous Silicas Followed by 1H NMR

Abstract

Liquid-phase 1H NMR measurements of M41S synthesis gels were performed to characterize the structure of the alkyltrimethylammonium salt micelles swelled with benzene or trisubstituted aromatic compounds. The chemical shift and the line width of the aromatic species allowed the determination of the locus of the aromatic compounds within the templating micelle. Benzene is incorporated and immobilized close to the surface of the micelle, whereas the more hydrophobic trisubstituted aromatic compounds are located in the hydrophobic core of the micelle, where they retain some mobility. The variation of the amount of the aromatic swelling agent further supports this idea. The decreasing mobility of the alkyltrimethylammonium surfactants in the course of the synthesis could be followed from the broadening of the signals in 1H NMR. It showed that the organic−inorganic mesophase is formed within the first 24 h of synthesis.