IN-SITU EPR STUDY OF SOL-GEL PROCESSES

The electron paramagnetic resonance (EPR) spectra of the stable free r adical (4-oxo-Tempo) were investigated during sol-gel-xerogel transiti on both for non-doped and o-phenanthroline-doped silica glasses. Gradu al changes in linewidths, rotation correlation time, isotropic hyperfi ne interaction parameters and integral line intensities were observed. These spectral changes reflect variations in the composition, effecti ve viscosity and polarity of the cage media in the vicinity of the pro be. The EPR spectroscopy of stable free radicals as paramagnetic probe s is demonstrated to provide a non-intrusive in situ means to monitor structural and chemical changes during sol-gel glass formation.