The electron paramagnetic resonance (EPR) spectra of the stable free radical (4-oxo-Tempo) were investigated during sol-gel-xerogel transition both for non-doped and o-phenanthroline-doped silica glasses. Gradual changes in linewidths, rotation correlation time, isotropic hyperfine interaction parameters and integral line intensities were observed. These spectral changes reflect variations in the composition, effective viscosity and polarity of the cage media in the vicinity of the probe. The EPR spectroscopy of stable free radicals as paramagnetic probes is demonstrated to provide a non-intrunsive in situ means to monitor structural and chemical changes during sol-gel glass formation.
Bibliographical noteFunding Information:
The authors would like to thank Dr E.M. Kunoff (BGU) for helpful discussions and friendly support in the manuscript preparation. This research was supported by grants from the Ministry of Immigrant Absorption and Ministry of Science and Technology (Israel), and Forschungszentrum fur Umwelt und Gesundheit GmbH, Neuerberg (Germany).