The Effects of inorganic complexes or ions on the mechanical properties of nafion

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Title: The Effects of inorganic complexes or ions on the mechanical properties of nafion
Author: Berdine, Jennifer
Abstract: Nation is a perfluoro-sulfonate anionomer. Free-standing and solution cast membranes of Nation have been shown to preferentially incorporate large hydrophobic cations from either aqueous or nonaqueous solutions. The specific type of ion or ionic complex incorporated into the membrane determines the chemical and structural properties of both the - CF2- backbone region and the ether region of Nation. Nation has been used extensively to prepare biosensors and chemically modified electrodes for electrochemical analysis in both classical and chromatographic detection. The physical and chemical effects that an incorporated species could have on film modified electrodes needs to be characterized. The goal is to establish long term mechanical stability and signal reproducibility of Nation chemically modified electrodes. In this study, freestanding H+ Nation films were exposed to a series of alkali, alkali earth, and transition metal cations. The study also included a preliminary investigation of complex inorganic and organic cations and their effects on the viscoelastic behavior. Several experimental procedures for preparing the freestanding films were implemented in order to study the overall effects that the different cations could have on the Nation films. The first set of conditions guaranteed a high level of neutralization within the films with respect to the incorporation of ions. Dynamic mechanical thermal analysis of the films then established the extent that the various counter-ions alter the mechanical properties of Nation. It was found that varying the temperature at which the films were dried after exposure to the aqueous and non-aqueous solutions controlled the amount of water retained in the membrane. Water content in the membrane also was dependent on the hydration characteristics of the counter-ion being incorporated. The dynamic thermal mechanical studies have shown Nation to have three distinct regions: a fluorocarbon region, an interfacial region and a region of ionic clusters. Charge density, size, and entropy effects were among the characteristics of the counter-ions that helped to establish which region they would be located after exposure. A second set of experimental conditions that resulted in the partial neutralization of the Nation films were also used. The dynamic thermal mechanical analyses indicate the creation of heterogeneous cluster regions within the ionomeric membrane.
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Date: 1998-07

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