STUDY OF SOL-GEL GLASS-FORMATION AND PROPERTIES BY PARAMAGNETIC PROBES

Two types of silica glass doped by o-phenanthroline (o-phen) (S2) and without organic reagent (S1) were studied. Paramagnetic probes (Mn(II) , VO(II), Cu(II)) were introduced into both systems by doping or by im pregnetion. Sol-gel-xerogel transition in these systems was investigat ed by electron paramagnetic resonance (EPR). In the S1 system, hydrate d metal ions were shown to react weakly with silanol groups during eve ry stage of silica polymerization. The effect of sol to gel transition is not observed in S1 spectra. Contrary to that, EPR spectra of VO(II ) ions in S2 demonstrate significant changes during sol-gel-xerogel tr ansition. As polymerization proceeds, the signals of non-immobilized h ydrated metal ion and that of mixed water-o-phen-metal complex are sub stituted by signals of metal-o-phen complexes immobilized on the porou s surface. After gelation, the latter signals prevail. EPR spectra pro vide a means to monitor in situ structural changes during the various stages of glass formation.