[PERFLUOROSULFONATE IONOMER] [SIO2-TIO2] NANOCOMPOSITES VIA POLYMER-IN SITU SOL-GEL CHEMISTRY - SEQUENTIAL ALKOXIDE PROCEDURE

In situ sol-gel chemistry was used to create inorganic/perfluoro-organ ic hybrids wherein titanium oxide outer regions of SiO2[1-x/4](OH)(x) nanoparticles, which were preformed in Nafion(R) membranes, were creat ed by postreaction with tetrabutyltitanate (TBT). U-shaped Si and Ti d istributions across the membrane thickness direction were determined v ia x-ray energy dispersive spectroscopy. Ti/Si ratio profiles are also U-shaped, indicating more Ti relative to Si in near-surface regions. IR spectroscopy verified structural bonding of TiO4 units onto SiO2 na noparticles and indicated that alkoxide hydrolysis is not complete. Re acted silicon oxide nanophases retain the topological unconnectedness possessed by the corresponding unreacted phase. IR bands signifying mo lecular loops and linear fragments of Si-O-Si groups are seen. Si-29 s olid-state NMR spectroscopy indicated that, for an inorganic uptake of 16.3 wt %, the Q(3) State of SiO4 is most populated although Q(4) is only slightly less prominent and Q(2) and Q(1) are either small or abs ent. The silicon oxide component, although not being predominantly lin ear, retains a measure of uncondensed SiOH groups. Tensile stress vs. strain analyses suggested that TBT postreaction links nanoparticles, c ausing them to be contiguous over considerable distances. This percola tive intergrowth occurs in near-surface regions generating a glassy zo ne. (C) 1996 John Wiley & Sons, Inc.