Measurements of the electrical conductivity and proton and fluorine-19 NMR spin−lattice relaxation times (T 1) in acid form NAFION 105, 117, and 120 conditioned at various levels of relative humidity have been carried out. Complex impedance studies were made along the plane of the polymer film at frequencies from 10 to 108 Hz at room temperature and pressures up to 0.3 GPa. The NMR measurements were made at room temperature and pressures up to 0.25 GPa. Both types of measurement were also carried out on various concentrations of sulfuric acid in water. The electrical conductivity decreases with increasing pressure for low water content acid solutions and low water content NAFION samples. This behavior (positive activation volumes) is that expected for “normal” liquids and for ions in polymers where the motion of the ions is determined by the host matrix. However, for high water contents, the reverse is true. The electrical conductivity increases with increasing pressure which gives rise to a negative activation volume. The results show that at high water contents, the electrical conductivity mechanism in NAFION is essentially identical to that for a dilute acid where the transport is controlled by the aqueous component. The activation volumes extracted from the proton NMR T 1 data are in qualitative agreement with those obtained from the electrical conductivity measurements at intermediate and low water contents, suggesting that motion of the sulfonic acid-terminated pendant chains contributes to the conduction mechanism at low water contents.

No abstract

No abstract

The relative permittivity and dielectric strength have been determined for a bisphenol A polycarbonate (BPA-PC), in which a cyanoethyl group has been substituted for one of the geminal dimethyl groups. The new material (CN-PC) has a glass transition temperature that is 19 K higher than that for BPA-PC. In addition, the dielectric strength of CN-PC, 405 V/μm, is somewhat smaller than that for BPA-PC, 620 V/μm. The relative permittivity was determined from 10 to 10 5 Hz over a wide temperature range and at pressures up to 0.25 GPa. While the real part of the relative permittivity at 10 3 Hz and room temperature for BPA-PC is about 3, that for CN-PC is found to be greater than 4. Correspondingly, the γ relaxation region in CN-PC is very strong. For the γ relaxation, a strong increase in peak height as temperature increases and a strong decrease in peak height as pressure increases are observed. A relaxation is found at temperatures higher than the γ relaxation. This process is labeled as the β relaxation because it appears to be related to the β relaxation in BPA-PC in that the strength and position depend on the history of the material. The effects of pressure on the γ relaxation for both CN-PC and BPA-PC are quite large and similar to those previously seen for the γ relaxation in a fluorinated tetraaryl bisphenol A polycarbonate (DiF p-TABPA-PC). In fact, the activation volume is found to be approximately the same for all three BPA-PC-based materials despite wide variations in both peak position and peak height. Finally, computer studies of the model compounds, 4,4′-diphenylpentanenitrile and diphenyl carbonate, were carried out. Both provide insight into the nature of the γ relaxation with the latter yielding an activation volume in approximate agreement with the experimental values.

Audio frequency electrical conductivity and relaxation studies have been carried out on Parel 58 elastomer and Parel 58 elastomer complexed with a variety of lithium salts. The measurements have been carried out in vacuum over the temperature range 5–380 K and at pressures up to 0.65 GPa over the temperature range 230–380 K. Both the electrical conductivity for the complexed material and the electrical relaxation time associated with the α relaxation in the uncomplexed material exhibit VTF or WLF behavior. From a VTF analysis for both the vacuum electrical relaxation time and electrical conductivity, Ea is found to be about 0.09 eV and T0 is found to be about 40 °C below the ‘‘central’’ glass transition temperature. In addition, it is found that the activation volumes for the electrical relaxation time and the electrical conductivity are the same when compared relative to T0. These results imply that the mechanism controlling ionic conductivity is the same as that for the α relaxation, namely large-scale segmental motions of the polymer chain.

No abstract

No abstract

No abstract