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 system. Tetramethoxy orthosilicate (TMOS, Si(OCH3)4) was used as an alkoxide precursor. The long-range ionic transport was studied by impedance spectroscopy, and local dynamics of molecules were monitored by polarized-light spectrofluorimetry. A slow, but steady decrease of the ionic conductivity and a similar time-dependence of the reciprocal microviscosity were observed during the sol–gel process. The changes of local and long-range transport properties are ascribed to interactions of molecules of the pore liquid with highly ramified surfaces of pore walls and to geometrical constraints on the freedom of their local motion.