EPR investigations on the formation of micelle-templated silica

The mechanism of formation of aluminium-containing micelle-templated silica s (MTS) was investigated by in situ EPR combined with XRD. Analysis of the spectra of EPR probes. 4-alkyldimethylammonium-2,2,6,6-tetramethylpiperidin e-1-oxyl (CATm), allowed the monitoring of the synthesis of MTS at 343 K in the presence of alkyltrimethylammonium bromide (C(n)H(2n+1)1 N+ (CH3)(3) B r- = nTAB) surfactants with hydrocarbon chains from 8 to 18 carbon atoms. T he kinetics of MTS formation is strongly dependent on the surfactant chain length, larger micelles inducing a faster MTS formation. Furthermore, the f raction of CATm probes strongly interacting with polar sites on the silica surface increases by increasing the chain length. The hydrophilic-hydrophob ic balance of the surface was correlated with the structure of the hexagona l pores, allowing the characterization of hydrophobic corners and hydrophil ic sides. (C) 2001 Elsevier Science B.V. All rights reserved.