EPR investigations on the formation of micelle-templated silica

The mechanism of formation of aluminium-containing micelle-templated silicas (MTS) was investigated by in situ EPR combined with XRD. Analysis of the spectra of EPR probes. 4-alkyldimethylammonium-2,2,6,6-tetramethylpiperidine-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) Br- = nTAB) surfactants with hydrocarbon chains from 8 to 18 carbon atoms. The kinetics of MTS formation is strongly dependent on the surfactant chain length, larger micelles inducing a faster MTS formation. Furthermore, the fraction of CATm probes strongly interacting with polar sites on the silica surface increases by increasing the chain length. The hydrophilic-hydrophobic balance of the surface was correlated with the structure of the hexagonal pores, allowing the characterization of hydrophobic corners and hydrophilic sides. (C) 2001 Elsevier Science B.V. All rights reserved.