Showing papers by "Kenneth A. Mauritz published in 1996"

Asymmetric nafion/(zirconium oxide) hybrid membranes via in situ sol-gel chemistry

Abstract: Nafion-in situ sol-gel reactions were affected for Zr(OBu)4 that permeated low water content membranes unidirectionally. IR peaks reflecting ZrO2 and incomplete hydrolysis of ZrOBu groups near both surfaces were detected. Vibrations of Zr(OEt)4 detected near both sides arise from alkoxy exchange in the presence of the solvent EtOH. Unreacted alkoxy group bands are more distinct near the nonpermeated surface. An IR band for the ZnOBu group diminishes, whereas that for ZnOEt increases with increasing time near the permeated surface due to progressive alkoxy exchange. The ZrO2 band becomes more intense with time near the permeated surface. X-ray spectroscopy/scanning electron microscopy studies of Zr concentration across the membrane thickness verified compositional asymmetry. CO2 gas permeability versus upstream pressure plots are monotonically increasing, suggesting diffusion accompanied by complex plasticization. © 1996 John Wiley & Sons, Inc.

[Perfluorosulfonate ionomer]/[SiO2‐TiO2] nanocomposites via polymer‐in situ sol‐gel chemistry: Sequential alkoxide procedure

Abstract: In situ sol-gel chemistry was used to create inorganic/perfluoro-organic hybrids wherein titanium oxide outer regions of SiO2[1—x/4](OH)x nanoparticles, which were preformed in Nafion® membranes, were created by postreaction with tetrabutyltitanate (TBT). U-shaped Si and Ti distributions across the membrane thickness direction were determined via 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 nanoparticles and indicated that alkoxide hydrolysis is not complete. Reacted silicon oxide nanophases retain the topological unconnectedness possessed by the corresponding unreacted phase. IR bands signifying molecular loops and linear fragments of Si(SINGLE BOND)O(SINGLE BOND)Si groups are seen. 29Si solid-state NMR spectroscopy indicated that, for an inorganic uptake of 16.3 wt %, the Q3 state of SiO4 is most populated although Q4 is only slightly less prominent and Q2 and Q1 are either small or absent. The silicon oxide component, although not being predominantly linear, retains a measure of uncondensed SiOH groups. Tensile stress vs. strain analyses suggested that TBT postreaction links nanoparticles, causing them to be contiguous over considerable distances. This percolative intergrowth occurs in near-surface regions generating a glassy zone. © 1996 John Wiley & Sons, Inc.

Asymmetric [Nafion]/[silicon oxide] hybrid membranes via thein situ sol-gel reaction for tetraethoxysilane

Abstract: Asymmetric silicon oxide composition profiles along a direction perpendicular to the plane of Nafion® sulfonate films were created via in situ sol-gel reactions for one-sided tetraethoxysilane permeation, as verified by EDAX/ESEM. For K+ form membranes, we propose the existence of an IR spectral signature of molecular branches in addition to those characteristic of linear and cyclic fragments in the silicon oxide phase. The molecular structure of the silicon oxide phase is more interconnected than linear in K+ form membranes. For H+ form membranes, there appears to be an increasing degree of molecular linearity within the silicon oxide phase with increasing uptake. IR spectra indicate that molecular connectivity on the permeated side is lower, on the average, than that on the nonpermeated side. The inverse relationship between gas permeability and upstream pressure in steady-state helium gas transmission experiments suggests the dual-mode sorption of gases, which is in harmony with the multiphasic nature of these membranes. © 1996 John Wiley & Sons, Inc.

Small-Angle X-ray scattering studies of Nafion®/[silicon oxide] and Nafion®/ORMOSIL nanocomposites

Abstract: The small angle X-ray scattering technique was used to probe structural heterogeneity on the scale of nanometers within Nafion®/[silicon oxide], Nafion®/[ORMOSIL], and Nafion®/[dimethylsiloxane] hybrid membranes. The results of this study reinforced the working hypothesis of morphological template action for the in situ growth of silicon oxide, or organically modified silicon oxide phases in perfluorosulfonate ionomers via sol-gel reactions for silicon alkoxide or/and silicon alkylalkoxide precursors. Nanophase separation persists when incorporated silicon oxide particles are postreacted with ethoxytrimethylsilane but postreaction with diethoxydimethylsilane generates co-continuous phases that do not generate ionomer SAXS peaks, presumably due to a more homogeneous Si atom distribution within the ionomer. These hybrids are true nanocomposites, as structural heterogeneity exists on the scale of ∼ 5 nm. The variation of the small angle upturn for these hybrids is explained in terms of long-range inhomogeneities in ionomers. © 1996 John Wiley & Sons, Inc.

Novel Nafion®/ORMOSIL hybrids via in situ sol-gel reactions: 2. Probe of ORMOSIL phase nanostructure by 29Si solid state NMR spectroscopy

Abstract: Perfluorosulfonic Acid (PFSA)]/[Organically-Modified Silicon Oxide (ORMOSIL)] hybrids were formulated via sol-gel reactions of mixtures of tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEDMS) in the nanophase-separated morphology of a PFSA membrane (Nafion®) The molecular structures of the ORMOSIL phases were investigated by 29Si solid state NMR spectroscopy and the spectra compared with those of corresponding bulk ORMOSILs PFSA-in situ ORMOSIL composition can be tailored by manipulating TEOS/DEDMS source solution composition and quantified by 29Si solid state NMR spectroscopy Copolymerization of TEOS and DEDMS monomers, rather than block formation, occurs within the PFSA as well as in the bulk As DEDMS feed concentration increases, ORMOSIL nanostructures are more hydrophobic and more flexible Dimethylsiloxane rings are dominant in PFSAs in which hydrolysis + condensation of pure DEDMS occurs