Ionic conductivity of silica gels and dynamic properties of their pore liquids studied by impedance spectroscopy and polarized-light spectrofluorimetry

Long-range transport and local molecular motions in the sol/gel system have been studied during an acid-catalyzed sol-gel process in the silicate syst em. Tetramethoxy orthosilicate (TMOS, Si(OCH3)(4)) was used as an alkoxide precursor. The long-range ionic transport was studied by impedance spectros copy, and local dynamics of molecules were monitored by polarized-light spe ctrofluorometry. A slow, but steady decrease of the ionic conductivity and a similar time-dependence of the reciprocal microviscosity were observed du ring the sol-gel process. The changes of local and long-range transport pro perties are ascribed to interactions of molecules of the pore liquid with h ighly ramified surfaces of pore walls and to geometrical constraints on the freedom of their local motion. (C) 2000 Elsevier Science BN. All rights re served.