Electron Paramagnetic Resonance
An EPR tool box for exploring the formation and properties of ordered template mesoporous materials
Published:16 Dec 2008
The formation of templated mesoporous materials (TMM), where highly ordered mesoporous materials are prepared using surfactant self-assemblies as templates, is an intriguing process. It depends on a delicate interplay between several concomitant basic processes; the self-assembly of the surfactant molecules forming structures that serve as templates, the sol-gel chemistry that generates the inorganic silica network, and the specific interaction at the interface between the organic and forming inorganic phases. In this review we briefly describe the properties of TMM and review some basic principles underlying their formation mechanism. After a short description of the various methods that can be used to investigate the details of such reactions at the molecular level and the mesoscale we focus on the unique contribution of various EPR techniques. This is achieved by introducing nitroxide spin-probes, designed to examine different regions in the forming mesostructure, into the reaction mixture. Continuous wave (CW) EPR measurements, carried out in situ, give information on the polarity and microviscosity in the close environment of the spin-probe. These are complemented by electron-spin echo modulation (ESEEM) experiments that follow the water content, presence of additives and interaction with ions and provide an understanding of their effect on the structure of the final material. Finally, double electron-electron resonance (DEER) measurements are used to explore size variation of the micelles during the initial stages of the reaction.