[Perfluorosulfonate Ionomer]/Silicate Hybrid Membranes via Base-Catalyzed In Situ Sol-Gel Processes for Tetraethylorthosilicate

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Polymers and High Performance Materials


Base-catalyzed sol-gel reactions for tetraethylorthosilicate were conducted within Nafion(R) sulfonate membranes. Silicate percent mass uptake, for all counterion forms and imposed conditions, decreases with increasing pH. Environmental scanning electron microscopy-EDAX studies of the distribution of silicon across the Nafion(R) membrane thickness direction revealed rather uniform concentration profiles except for upturns or downturns in the near-surface regions and demonstrated that it is possible to incorporate silicate structures deep within these membranes. Si-29 solid-state NMR spectroscopic studies revealed that, for Li+ and Na+ counterion forms, bonding in the silicate phase is such that there is more intra-molecular coordination at high pH. FT-IR spectroscopy uncovered all the signature peaks characteristic of silicate structures in the near-surface regions. Fingerprints of Si-O-Si groups in cyclic and linear molecular substructures, as well as SiOH 'defects' are present. The spectra of Li+ form hybrids reflect a silicate network that becomes increasingly more interconnected with increasing pH, in harmony with the NMR results. The relationship between the spectroscopic information, porosity of the silicate phase, and possible permselectivity based on a molecular-sieving effect, is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

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Journal of Membrane Science





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